I don't have numbers, but I'd be willing to guess that a fair number of IE6, 7, and 8 users were on corporate PCs which prohibited installations of newer versio

I don't have numbers, but I'd be willing to guess that a fair number of IE6, 7, and 8 users were on corporate PCs which prohibited installations of newer versions of IE or other browsers. Microsoft can't do anything about those people! They have been try to end support for Windows XP and IE 6 for years, and newer versions of IE auto-update unless the user specifically tells the OS not to.