sorry but what do you mean by " The newest version of IE can't even be run on Windows 7. "
what version is that ? I am running a build of IE10 on windows 7 right now. it is a preview build and the final is coming. works fine for almost all sites I go to. the problem ones are the ones that for example refuse to see that this is IE10 and not IE 6 /7/8.
I meant at this time and I don't count the preview because the general population typically doesn't use prelease software (nor should they if they expect it to run at a production release standard). IE10 is released for Windows 8 but there isn't a RTW version for Windows 7 yet and there won't be one for Vista or XP. My point is, if you're using XP or Vista and want to use a current browser you have to look elsewhere and because of this IE will bleed market share.
On the topic of IE, every other top tier browser that has a version that supports Windows 8 also supports Windows 7 today, how is Microsoft so far behind with their own browser on their own OS? These are the contributing common sense reasons why IE is bleeding market share.