"If this is true, it's *extremely* dumb of Microsoft at a time when they are hoping to sell more units of Vista/Windows 7 than they did of XP."
Well, I'm just a scientist, not some business type, but this sounds like a smart move.
Who upgrades their OS, specially in the Windows world? You know, go to a store and buy a box and then do all the incantations? I don't know about enterprise, but in academia I can tell you: nobody. At home it is pretty much the same, I suspect. When the machine falls apart (or rather: is perceived to do so, when it's actually just Windows bit-rotting, but I digress), people buy a new machine. Which comes with Windows installed on it, unfortunately, and that isn't going to change anytime soon. So, there goes another Windows sale, as has been for a long time now. Then people use the thing (and complain that it looks a little different, blah, blah), and install their old programs on it. And if everything still runs, yay!, and the old OS is forgotten. If not, see Vista's history and its resulting reputation (regardless of it being deserved or not, which is another story). Same will go for developers, I think. The developing tools will be geared towards the new OS, so why not use them as they are, since the users are all adopting the new OS anyway, since it seems to work exactly as before?
So, if this works well and easily for the computer illiterate as well, it should be a success. Mucking as little as possible with the user interface always helps too, of course.