My two cents....
If any of you have seen Vista you'd know that the biggest upgrade needed for most PCs will be graphic cards. Vista runs fairly well other than that. Sure, a fair amount of memory and a decent processor are required.
I sometimes upgrade and build computers for people when I have the time. When they bought their computer, even recently, most comp stores don't scrimp on the memory or processor because those are the things people know about. Every Joe Schmoe off the street tells me that their computer has 2 gig of memory and a 3+ gig processor. The cheap box computers that you buy for $600 come with a great processor and at least a gig of RAM. That is plenty for Vista, but they also come with an on-board 126MB (or less) graphic card, because most people don't know the difference. Unless they are into 3D gaming they would never be able to tell.
Then vista enters the world. The average computer will be able to run Vista, but only after they upgrade to at least a 256MB (and preferrably higher) video card.
So to make a really long story just a bit shorter. The decision to buy ATI was probably a good move. AMD was getting squeezed by Intel. When I build computers for people and I ask if they want an AMD or an Intel platform, they always say that they heard AMD is better. Then I tell them the price difference and they always go with Intel. When it comes down to it folks, Intel offers more product utility for the price.
Combine with that the fact that there are many apps out there that won't run properly on an AMD system.
That said, I do find it odd that Apple is at highs right now while AMD is at lows.