I play in a group of 6 (including me).Yeah, the release schedule stuff that is so important to many on here is not even something that is even remotely thought about by my group. They are just "is this game fun to play".
The one who has been playing RPGs the least amount of time has been playing for over 15 years (since I got him into Rolemaster in early 1998).
So I think we count as a fairly serious group.
We have two active campaigns: a 4e one, and a Burning Wheel one.
I own around 40 4e books, mostly hardcover. Of the others, all but one owns a PHB. I think there is also one PHB2, and one PHB 3. The fighter player has a Martial Power, the paladin player a Divine Power, and the sorcerer play an Arcane Power. I think two of the players also have DDI subscriptions.
WotC's release schedule is basically irrelevant to us. While they were publishing stuff that appealed to me, I bought it. Stuff they published that didn't appeal to me (eg Draconomicons, Eberron) I didn't buy. The others bought a bit of stuff relevant to their PCs, but that's it. Playing the game is about turning up to sessions ready to have fun, plus some character maintenance between sessions (for about half the players that's fun, for the others it's sometimes a chore).
As for Burning Wheel, there are only 6 books to own (5 books in Revised, plus the Gold hardback). I own all of them. One other player owns Gold and two Revised supplements. We shared these books to support PC creation, and the others play using "cheat sheets" that I wrote up. Luke Crane's release schedule (which as far as I know is now focused on Torchbearer) is irrelevant to us.
If WotC published another 4e book that took my fancy, I'd buy it (I have the money). If Luke Crane published another BW book, I'd snap it up (I have the money, and I think he writes the best RPG rule books around). But the availability of those books for purchase is pretty orthogonal to the games I'm wanting to run.
The only other game I've run in the past couple of years is Marvel Heroic RP. That's another game that's out of print, another game I ran for players who had no books (they used a cheat sheet I'd written up), and another game I'd happily play for an extended period without worrying about a (non-existent) release schedule.
I think there must be a lot of groups more casual than mine for whom release schedules are equally irrelevant.