I don't know if I'd go with the theory that MS doesn't need to make money. They're beholden to stock holders, and stock holders expect a profit. If they don't get a profit, they are no longer stock holders, and then the company's value decreases, and eventually that theory about being able to live off interest goes out the door. It's not like all that value is in cash, not like throwing money in a bank account with a guaranteed interest rate.
Anyway, that's neither here nor there.
If whatever it is you have works for you, go with it, but, yes, be careful of such "gifts."
An interesting aside that came to mind because of this:
Due to Alfredo's inspiration over in the OpenSource group, I started messing with
VirtualBox. At length, I got curious and installed a virtual Vista machine on my Linux host. There were some niggles getting it working. The network didn't want to come up on the initial install. I had to allocate 1 gig of my memory for the system and another 128MB of it to video memory to get it to work decently, had a bit of trouble with shared folders on my Linux host, but other than that, it all went smoothly. And it's interesting to play with. At the very least I've been able to work out a few issues others I know are having with their Vista machines that came off as Greek to me when they described them because of my unfamiliarity with the Vista interface.
I still don't like it, but I'll let it sit in its jail on one of my drives and bring it up if the need ever arises.
OnEdit: As to the original question, I have no proof of this and am certain no Microsoft exec would ever admit it openly, but my own theory is that they've given up on Vista and are focusing on Windows 7 now.