Or it could be that peoples expectations have changed.
Technology progresses, there is constant advancement. After Windows 95, there was 98, which was better, but 2000 was the real deal, stabled, rock solid as long as you didn't poke it too much. XP was initially a step back, heaps of issues, slower, but new features, over time the issues got resolved and turned it into a solid reliable OS. I've been using XP as non-admin for a long time now, and time between reinstalls is in years for me.
Vista on the other hand, is a step back, heaps of issues, but no significant features! That final part is the real issue, if Vista had shipped with all the features that were initially promised, the performance hit might have been justifiable.