Windows 7 doesn't crash anymore. If we are talking about Vista or XP then ok, but 7 is really rock solid.
The problem is related to drivers that make Windows crash (we all know the nature of the interaction among drivers and an OS meant to be run on a big variety of different hardware (aka Windows)).
ATi didn't make good quality drivers for its graphics cards in the past. Now their drivers are very good and the stability of the system is increased, and the graphics performances are awesome.
In the same manner Apple isn't making out good quality drivers for their hardware, and so the stability and the performances of a Windows OS running on this hardware is compromised!
In the beginning Vista was crap which is why it has a bad reputation for it's stability, but now it's hardly the case, it's extremely stable.
I hate Vista, but it's not for it's stability. Vista is rock solid now.
( it's funny that Windows 7 in a Virtual Machine under Linux runs faster than Vista. That pretty much says enough how slow Vista actually is )