Let me try restating my point: Windows users know how to be productive in Windows. How many of these people will be willing to give up that knowledge for a Mac that may be faster in terms of brute speed but with which they will, at least initially, have no idea how to be productive with?

Sit a person who's only ever used Windows their whole life in front of a Mac and ask them to find and launch a certain application. Once they realize there's no Start button they'll probably be completely lost.