"It is the default browser shipped with Windows XP and Windows Server 2003, and was also made available for Windows NT 4.0, Windows 98, Windows 98 SE, Windows Me, Windows 2000, and Windows Home Server (a derivative of Windows Server 2003). IE6 SP1 is the last version of Internet Explorer available for Windows NT 4.0, Windows 98, Windows 98 SE, Windows Me, and Windows 2000. Although Internet Explorer 6 was superseded by Internet Explorer 7 in October 2006, Microsoft still supports it in Windows XP SP3."
Once you start dealing with big corporations, it's not as simple as "oh it's time to update".
I do not see the point of worrying about this. If enterprise (put forward as the major user of these) is the worry then you might have to care. If it's random users that just don't feel like running Windows Update, well, these people aren't going to be spending much money anyway.
Worrying about [insert version of IE here] hanging around forever seems to be nothing but complaining for the sake of complaining now that IE6 is completely out of the picture.