Stumblewyk
Adventurer
Eh. I don't know about this so much...well, maybe I do, but there is a caveat. Maybe I'm just lucky, but in my one gaming group, we've got 6 people - 4 of us are GMs.The problem is that in fact, there aren't that many tables because there aren't that many game masters. The number of willing players exceeds both the number of willing dungeon masters.
In my other group, we have 7 people, I DM primarily, but 2 others have taken the helm from time to time to give me a break.
I think there are plenty of DMs out there, we just tend to group up with like-minded gamers.