The version of T-Mo's 2.2 was leaked awhile back (Been running it since it came out, in fact), so most likely it'll be out (I'd imagine before the end of the year)
As for Samsung being behind, checking on Androidspin and XDA-Dev's news, there are a LOT of phones by a LOT of manufacturers that are still either running 2.1 or are JUST NOW GETTING 2.1, so Samsung's not really any more guilty than the rest. They all suck at OS updates :-/
That being said, I don't know why Samsung would bother with 2.2, since 2.3 is "right around the corner". Maybe that's why they've decided to hold off. Who knows. Doubtful. The official 2.2 will probably be out in the next couple of weeks, just in time for everyone to start crying "Where's 2.3?!?!?"
2.2 runs fine on the Vibrant as it stands now, so I've got no complaints.