Answer: lots and lots of people. New post up on Seattle 2.0 :
[T]he fact is that, even with years of (public) neglect, there were hundreds of millions of desktops which required IE working exactly as IE had always been. And this was the blessing and a curse that underlies where IE is today. >>>
In the world of the Web, where people constantly focus on the new new thing, there are worse places to be than majority having hundreds of millions of users as an installed base.