The fact that Microsoft keeps changing the basic support of their OSs each year is dirty. If they had any competition with OSs that were capable of running programs with the same source code, the situation would be very different. Instead we'd get an OS that was updated each year but didn't lose support so quickly, and was given more interface improvements over the course of it's life.

Instead, Windows 2000, XP, Vista, are all very similar in their source codes. The major differences are external and shouldn't require us to upgrade or risk "support" and availability of the versions we like.