IE6 is packaged with XP. A large part of why it's around is that people who bought XP couldn't be arsed to upgrade to anything better.
If some corporate IT department wants to upgrade to Windows 7 but still reinstall IE6 over it for some crufty legacy app compatibility, I think they'll probably have much bigger problems that would make the OS upgrade pointless altogether.
Granted, Windows 7 currently ships with IE8, so we'll still have the same problem for a while.
They will have to install ie6, some of them anyway, because there are a TON of applications out there built to IE6 that are years old with no one to support them and many of them have code bases that have disappeared.
It's a sad situation really. It's easier to install IE6 than rewrite the apps to work with another browser.
Targeting IE for "web" apps resulted in unupgradable windows-only apps plus a lie. The lie that they were "web apps". A cautionary tale about Microsoft lock-in causing damage to the web and to IT as a whole.