Top-Down Disruptions?

Strategy+Business magazine offers an interesting article that expands on the current work and thinking of Clay Christensen. What I found most interesting was the distinction between top-down disruptive innovations and grassroots innovations.

Christensen suggests that not only are top-down disruptions as powerful as their smaller scale, grassroots counterparts — but that they may be more easily created and sustained. This can give incumbents a competitive advantage.

What do you think? Is top-down or bottoms-up innovation more powerful?