I'd agree with your argument if I hadn't wasted months of my time (as a programmer) trying to find out why our software wasn't working only to discover that installing IE3 (for example) changed an event interface to call it three times instead of twice...
Look at any programming forum to find problems caused by sneak system file upgrades and api changes from installing MS software, and perhaps you'll feel sorry for the several million software developers outside of MS who spend most of their time working round bugs/changes in the different versions of windows.

You're lucky you work in the Mac division...

Jazz
(List 112, Mk2 12 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)