The best solution I see to the "no IE9 for windows xp" problem if were not counting on Microsoft to do something is Chrome frame; but I think some big player (youtube, facebook etc..) would have to almost force it on users for it to cut down on those big percentages
Yes, but there are plenty of other browsers such as Firefox and Chrome that work in XP. Unless you're talking about accessing sites that will work only in IE.
http://www.google.com/chromeframe