why use a top-of-the-line graphics chip for rendering Windows XP's UI, for instance?

Short answer... short question!

"why use a top-of-the-line graphics chip for rendering Windows XP's UI, for instance?"

And how many of these laptops will allow Windows XP? I'm already sick of hearing "we don't support XP in this laptop, and don't expect any XP support in the future"?

I've had this response from all major vendors (except HP)

Don't expect OEM to claim XP support in any of their new kit. When I bought my Compaq Presario last november, I discovered afterward that there are no XP drivers for any of the hardware in it. As of January 2009, no new systems will come with XP anyway.