It’s a pretty good idea–while using your Google search on an iPhone or Android device, related apps on your platform will show up at the top of the normal search results. You can tap on those links to take you directly to that app’s listing in whichever store you use. On an iPhone, this could be really useful–apps sometimes change names, or have difficult-to-remember names, and Google search might well be a better option than the built-in search in the App Store app.
On Android it’s a little more puzzling. Not that the Android Market is better designed than the App Store, because it most assuredly is not, but Android is a Google OS which heavily focuses on search. Surprisingly excellent voice search is built in to the OS. Every Android phone has to have a dedicated search button. So why would the Android Market’s search function be in need of replacement by another Google search?
But it’s still a nice option, one that most people will accidentally stumble across, but one that will leave most people pleased.