Oddly enough, I can't seem to find any lions running around loose.
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Thanks to Mr. Gardner, I've been doing quite a bit of reading on the free markets, labor, socialism, capitalism, etc. - I haven't reached an ultimate conclusion at yet, but I will report my conclusions here at a later time.
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That being said, I can only state my beliefs, based on over 20 years of work experience, and life in these here United States:
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1. In my lifetime, I've never witnessed a free market affect that improved the vacation time of the average American worker. As I stated before, if you lose your job due to forces beyond your control, whether you've worked for two years or twenty, your new job will offer you two weeks vacation, unless you are a teacher (and not everyone can be) or a seasonal worker (which generally means, you will have no benefits).
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2. Business has control over a workers UNDESIRED unemployment. It's true that a worker can elect to leave a job, and get a better job (it's up to the worker to define "better"), BUT a business can terminate the employment of an employee for both cause or no cause, without any warning. -In the first case, the employee will be left to their own resources; -in the second, unemployment will be paid for a period of time. - I invite Mr. Gardner and those who agree with him to find out exactly how much money unemployment will yield.
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3. If the free market truly served the needs of the workers, Labor Unions would have never been able to form or survive.
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4. There is no way to know the number of people who have avoided injury or death since the regulations imposed by OSHA. I do know my father worked in a steel mill, and prior to OSHA, you were given a pair of steel toed boots, a hard hat, some insulated gloves and goggles, and told to be careful. - Many of my father's friends were missing fingers, toes and limbs, burned off by the hot steel, as careful as they tried to be.
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5. - I do know that Labor Unions gained traction in the US at first because of the plight of mine workers. US mines existed for over one hundred years, and working conditions and safety improved at a snails pace. Within 8 years if forming the United Mine Workers, they had won an eight hour workday, and a number of safety improvements. From the period from 1890 - 1933 Over one hundred miners were killed and thousands were wounded withstanding strike breaking tactics.
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If the free market works, why did these people have to die?
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6. Free Markets are not always good, nor are they always bad. - But they exist in a moral vacuum, and workers are far more likely to suffer in market failures than employers.
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7. If we truly had free markets in the US, why should oil, tobacco, automotive, industrial farms, pharmaceuticals and other corporations get government subsidies?
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At this point, I'm leaning toward Martin J. Whitman who is an American investment advisor, and a critic of Friedman and Hayek. He states:
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"I am one with Professor Friedman that, other things being equal, it is far preferable to conduct economic activities through voluntary exchange relying on free markets rather than through coercion. But Corporate America would not work at all unless many activities continued to be coercive."

A good way to think of an economy is to think of a runner. Or perhaps two runners racing. One runner has a very overprotective doctor that insists on his athlete wearing various protective garments.
This runner has ankle braces, knee braces, a helmet, shoulder pads, and he’s eaten too much fiber because that’s healthy as well and so he’s feeling a little bloated.
The other runner is dressed as we would expect a marathoner to dress. Very little.

The overprotective doctor complains loudly about how badly treated that runner #2 is treated. “He is obviously lacking in health care; look! No knee braces!”
The less protective doctor feels bad because he wants to be liked by the international community.
So he slaps some knee braces on his runner.
And #2 slows down a bit.
The overprotective doctor smiles wickedly. “Look! The poor, oppressed runner has no ankle braces!”
And so the vulnerable and easily persuaded doctor for runner #2 slaps on some knee braces.
And #2 slows down a bit more.
And along comes runner #3. No braces, no helmets, nothing.
He’s whizzing right along, and though he’s not big and healthy and like #2, he’s able to quickly make ground because of his lack of “protective” gear.
All along, the overprotected runner, #1 we call him, he’s torn between trying to shed his own braces so that he can move easier, and persuading the other runners to adopt his own handicaps.
Then a lion somehow escapes, and everyone has to run for their lives.
Guess who gets eaten first?

Mandated vacations are part of the unnecessary padding of regulated markets. They strangle, slow and eventually kill.

Charles:
Sorry if I offended you. You seemed to be genuinely solicitous of answers, and so I obliged with good objective sources that are too lengthy to quote fully here.

More to the point however, the data you seek is the world and its economic history that lies at your fingertips.

America is the economic leader precisely because it is the freest market with the most natural and human resources. A small number of other economies are freer (Hong Kong, Singapore) but they lack our overall resources. Others possess our resources, but lack the internal infrastructure to prosper as America has.
Look at our poor.
A vast majority of American poor own a car, color television, VCR and/or DVD player, cell phone and they typically rent or own a house. And their homes and apartments have air-conditioning.
The average poor American has more living space than the average individual living in Paris, London, Vienna, Athens, and other cities throughout Europe. (These comparisons are to the average citizens in foreign countries, not to those classified as poor.)
And two-thirds of them have more than two rooms per person in these homes or apartments.

European markets can only compare to the American markets in narrow slices, and not as a whole. This is a lengthy subject and you should consult the FreeTheWorld website I listed earlier for very good reading on this subject.

For worker mobility, I am genuinely surprised that someone as well read as yourself doesn’t already know about the hot topic of American labor mobility.
It is a very hot topic, indeed, and although the opinions vary as to whether it’s a good or a bad thing, the ease with which “Gen X” workers move in and out of careers and between companies is simply astounding.
It has prompted many publications, and I would suggest simply Googling the subject and reading for awhile.

The American auto industry was undone by union labor, and New Deal era deals struck with the unions.

Major points:
As Rob mentioned, the other countries couldn’t field a team.
That means that the Americans didn’t have any real competition.
And what happened?
When Japan finally got a team together, the Americans were slow, sloppy and lazy.
Bottom line, without competition, cars were of much poorer quality than they had to be, much more expensive than needed, and the labor force producing them was growing ever more complacent, getting paid more and more for less and less skill and actual hours of work accomplished.
When the other teams did take the field, again – as Rob mentioned, American companies could not adjust quick enough because of labor agreements.
Ironically of course, the thing that was supposed to protect the worker, killed the worker.
This analogy of the American auto industry is a perfect microcosm of regulated economies.
Where government intervention is found, industry becomes slow and tied down by regulations that do not allow them to adjust to economic competition from abroad.
China and India have nothing approaching our labor laws, our OSHA standards, our environmental restrictions. When an American company tries to compete with that, they’re not just competing with a foreign company, they’re competing on totally different fields.
The need for competition and freedom for movement – both by the company and the worker – is essential for a healthy, dynamic and affluent economy.
Government mandated vacations run 180 degrees contrary to everything that makes the market free, and thus competitive, and thus everything that is eventually good for the individual laborer.

The US Auto industry did not fail because of government intervention. - The US Auto industry enjoyed a monopoly that was "an unsustainable anomaly", according to Stephen D'Arcy, head of Global Automotive Practice at PriceWaterhouse Coopers (as quoted in the BBC article "The decline of Detroit" 19-FEB-2007).
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If I recall correctly, Tom Peters, author of "In Search of Excellence" said that the US Auto industry won the "World Series of Automobile manufacturing" year after year, because nobody else could field a team. American automobile companies focused on larger, high margin vehicles, and were caught flat footed for demand of high mileage vehicles after the post 1973 oil embargo by OPEC.
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Admittedly, US Auto manufacturers could not cut their labor costs as quickly as they would have liked in the 1970's, but one could also make the case that this prevented massive auto worker unemployment, which in turn would have deepened the recession of the late 1970's, early 1980's.
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I don't think the demise of the US Auto industry was caused by workers getting more vacation. Rather, it was the result of both Business and Labor operating under a set of expectations, set in a market that no longer existed, both unable and unwilling to change rapidly enough to meet the demands of the new market.
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I might add, the US Auto industry was beaten by Japan and Germany, countries that have more direct government intervention in their economies than the US.

Thank you for educating me Mr Gardner however ,trying to show the other side of the coin should not mean recommending basic economics philosophys and readings to a discussant, it implies the discussant is not learned in economics, i would rather you submitt arguements and quote such authorities as backups, nevertheless i do not agree with your submission that labour simply shifts in the free market, that is the problem with theory, it may be to the point intheory but in practice workers do not easily switch jobs, infact if research were conducted a big proportion of the work force are not confortable with their curren employment but they find practical difficulty in switching, therefrom the view that labour simply switches jobs when opressed is with respect lacking in the domain of practiculity.
One could further opine that it would perhaps become counter productive to the free market model if job switching were as easy as suggested, consistency a hallmark of quality would probably become endangered if iam right and i think i could be.

In the third perspective it should not be forgotten by fellow discussants that much of Europe practices a similar free market system learned discussants allude to; wherefrom the explanation for why European employees benefit more vacation may not lay in the free market theory perse, for clarity much of Europe practices a similar free market system so why more vacation in one freemarket than another ? The discussion is still inconclusive and more suggestions are sought in good faith. Thank you.

Charles:
There's a lot to discuss in your comments so first let me recommend a couple of sources.
freetheworld.com is a economic think tank, based out of Canada, but with economists from several countries participating. They have made an index to judge the economic freedom of all of the countries in the world. (There's also one for North America.)
The index is objective as it doesn't contain any questionable measures, and the accompanying text would be very enlightening for someone like you.
The classic book on basic economics, "Economics in One Lesson" by Henry Hazlitt.
Also is the website CafeHayek.com; a daily blog kept by 2 econ professors from George Mason University.
There's obviously more sources, but those are a good start.
More on your last comment:
America is not a perfect free-market, but it is still relatively very free. Globally speaking, America is not lacking in this area.
It is impossible for companies to hold workers hostage in a truly free market, because in a free market, the worker is free to take his skills elsewhere.
This same free market also forces the companies to compete with each other so one cannot afford to not treat their employees poorly.
If Company A treats their people badly and pays them very little, then the best workers eventually gravitate to a better paying company. We'll call that company, Company B.
So Company A has trouble making a product that can compete with Company B because their workforce is inferior.
Company A eventually goes out of business, or pays for some higher skilled workers.
This in turn forces the worker to compete with other workers, and the circle of efficiency continues.
When the government gets involved and mandates higher pay, the system breaks down because the government is imposing a cost on the company that is not directly related to the demand for their product.
Those in favor of such government action will argue that such things have been done before without all of the companies going out of business.
But this is because the company simply passes these costs along to the consumer.
Eventually though, the consumer will look elsewhere for lower prices since the value of the existing product did not improve with that last price increase.
For a classic example of this; simply research the downfall of the American automobile industry through the 1970s and 80s.

The discussion is getting brilliant on the hour , a bystander would suppose in a free market system both parties to the bargain have fair freedom of choice, so why is it this freedom lacks in the American system, something must be wrong somewhere and perhaps it had better be adressed, simple as this appears, the discussion topic points to a fact that the free market the foregoing discussants praise will eventually need to be controlled otherwise the employer will hold the employee at ransom ... to some extent i must add, there is a right to holiday and this right is to the advantage of the employer as such an employee undertaking vacation normally would perform better, hence the current employment trend of less vacation may lead to deterioting innovation, among others for example. All said and done the market cannot be as free as some discussants would like ,that would endager the workers and a few years down the road we might discuss why American workers have less sleep, with respect markets and especially labour relations require reasonable regulation to avoid opression of the workers, that is what America must adress , less vacation is merely the beggining of the problem expected in a free market system.

And what does the Jefferson quote say first? - "...a wise and frugal Government, which shall restrain men from injuring one another..." - Business is not above doing injury in exchange for profit (don't forget, Jefferson was a slave owner).
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I think the argument you're trying to make is that government should not be involved in the regulation of business.
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However, ours is a government of and by the people, for the people. - Therefore, if the voice of the people, through their elected representatives, issues regulations on business for the benefit of the people, it is well within their right to do so.
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So why aren't the representative offices flooded with email and phone calls demanding a six-week paid vacation?
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In the first place, inertia - we don't even get half of our populace to vote in general elections. In the second place, Labor as a political force has grown continually weaker in the US (again, see "Union Busting" on Wikipedia to get that story). - I don't think it has much to do with "individualism" (and I'm not sure what that has to do with this thread anyway).
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Honestly, I think people live in fear for their jobs. Most people are less than a couple of paychecks away from serious economic harm. The fear of the loss of their jobs, and consequently their consumer goods, cars and homes keeps them from thinking about actually having better working conditions.

From Jefferson's first inaugural:
"Still one thing more, fellow-citizens—a wise and frugal Government, which shall restrain men from injuring one another, shall leave them otherwise free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned. This is the sum of good government, and this is necessary to close the circle of our felicities."

We don't demand of our government that they force private citizens to give to other private citizens that which is not the government's to give.
You might say that a spirit of individualism is part of the American DNA.