The #1 requirement in a graphics card is that it work. Fancy 3D performance? Don't give a whit. Out of the box the ATI video cards "just work" in my machines.
I've seen people mention that Microsoft spends considerable time with backwards compatibility, that Windows 7 hasn't broken a video driver, etc. ORLY?
I've moved to 64bit Linux ages ago. We're making the transition to 64bit Windows 7 at work. The list of hardware/software which just doesn't work is endless. Adobe Reader X? No "Open" option - provides "save only." The Diamond PCI video cards we bought for some staff to have dual monitors? No worky. Ditto for the business card scanners, older SCSI card based scanners, Sony voice recorders, etc.
I remember all too well when Windows installed and worked well yet Linux was a bear to get working right. Those days are long past. I have two scanners here, an Artec and an Epson V500. Both work just fine under Linux without any significant effort. The Artec on Windows 7 64bit? Not a prayer.
I do not game. Let's not delude ourselves that gaming drives the Linux market as it doesn't. I couldn't care less about gaming and neither does the biggest market for Linux: smart phones.