It's not just enterprise. For consumer websites the usage is going to hover around 3-5% (IE6,7,8 combined) for a long time - if you target less technically inclined people probably more. Tablets and Smartphones probably help more than Win7+ adoption in that area, but there's still going to be a significant amount of people using browsers on older computers.
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.