Microsoft have been pushing subscription based sales (activations, and licensing that expires after 12 months). Other products like Quicken do it successfully.
However for Microsoft to be able to force this profitable ongoing revenue stream down its enterprise customer's throats it will need them to actually USE the product.
Vista Flopped because it was too hard to remotely support (UAC being on by default made it very difficult to configure for RDP or Remote assistance, etc.) over an enterprise network. It made mundane tasks, excessive chores and meant a large cost for support that never existed with XP. My own employer developed an image for Vista for customer's environments before scrapping the idea as unworkable.
Simply put only through OEM licenses were Vista used and at the first chance, our company went back to XP for our customers and we still use it today.
Windows 7 doesnt look like it will be much better (from my early looks over the Beta)