One of the things about OS X is that most of the time it's put on high quality, but non-exceptional hardware. So things like bad RAM, flakey power supplies, bad GPU drivers etc are almost never an issue with a stock machine.

Windows, not so much. The only stability issues I've had with windows have been related to poor drivers, almost exclusively from nVidia or ATI/AMD. The equivalent hardware for Apple machines either didn't exist at the time, or was running much less ambitious drivers.

I probably have more issues with my Macbook Air (relating to sleep, hibernate, and wake-up) than I do with my Windows machines these days.