Not *really*, but it's an order of magnitude easier to coordinate a large-scale game with Steam than with various IRCs, vent servers, these forums...it seems to be the medium we use to do that. You can get one easily, it's free and such, and seems more common than, say, Xfire.
Go for it! This game may get too big and fail just because of sheer player size, but it might work. If that doesn't work, I'd go for a game with anyone in this thread.
Long story short, Steam is a hero.