IE9 auto-updates have been enabled for over a year, and IE8 has yet to fall to a single-digit percentage of page views... (Of course, IE8 share is kept high by the large number of users still on Windows XP, which won't be the case for IE9.)

http://www.tomshardware.com/news/Internet-Explorer-Windows-U...

As you stated, it's because XP has almost 40% Windows market share so IE8 will persist for quite some time.

http://en.wikipedia.org/wiki/Usage_share_of_operating_system...

It doesn't mean that most consumers won't take the IE10 upgrade. IE10 will be double-digit by this time next year.