I can see the debate both ways.
1) Apple's fault - Vista was fine before. iTunes 8 installed and now it crashes.
2) Microsoft's fault - The operating system should not go down because of a bad app. The app should abort and your operating system should continue to run. Vista is unstable. XP didn't crash.
It's not going down because of a bad app, but because of a bad driver. If it gives you a BSOD it's not even a proper Vista driver, but a legacy XP driver. It's no news that Apple can't be arsed to write dedicated Vista stuff, they're not even using DWM (Vista's equivalent of Core Graphics). All of Apple's Windows apps use oldschool XP style rendering, without drop shadows and other Vista specific bells & whistles, and are therefore very sluggish when scrolling etc.
Vista certainly leaves a lot to be desired, but one thing it does have is resilience to bad apps. It still can't do much against outright malware, of course, but as long as we're talking benign but poorly written software, Vista is pretty immune.
OS X on the other hand is quite vulnerable. I've had stuff like Logitech Control Center, DivX, Shapeshifter and certain hardware drivers (specifically, for the Yamaha 01X digital audio interface & mixer) screw up the system pretty bad. LCC wouldn't let me shut down or reboot; DivX would give me a blue screen for 5 minutes on every startup and the 01X driver caused a perpetual blue screen on startup. Stuff like this doesn't happen in Vista. It's more like the way that Windows 95/98 would behave.
Basically OS X is like the boy in the bubble, it has no immune system of its own, but thanks to the fact that it lives in a hardware environment controlled by Apple it's quite safe from harm anyway. But if some foreign object (such as bad 3rd party software) gets into the bubble, OS X just goes belly up and dies.
Vista lives outside the bubble, out in the rain among the street thugs, in a random hardware environment that Microsoft has no control over. But because Windows has endured so many years of hardware and software chaos, virus outbreaks and other crap, it's gotten pretty tough. It can still catch a cold every once in a while, but it will prevail.
