And it' is a shame they arn't bringing it out for winXP / Vista but it is understandable as XP may have more marketshare amongst there OS, but win7 is there new flagship so offcourse they are going to entice more people to move across to there newer OS.
AFAIK IE9 will work with Vista SP2?

If MS drop support for IE8, many people using XP are likely to go to a rival browser. I can't see people buying new kit just to run the latest version of IE, after all XP will run quite happily with much less resource than Vista or 7.

Also, I come across quite a few ex-corporate machines that have onboard video and no VGA slot so graphics would be a problem.