If the group I currently played with decided to move to 4e, I would essentially be out of a group, because I have enough fundamental problems with the system to never want to play it.
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The value of a "unified" player base/edition is that it gives players more overall opportunities for successful play.
I'm inclined to agree with Umbran on this issue.I'll make it really simple, sans analogy - you like only one game? That restriction is inside you, not outside in the rest of the world. It is your challenge. There's only so much the rest of the world can be expected to do to accommodate you. The world is not going to sit still and not look for new things because your tastes are inflexible.
Let's assume that a RPG group has two sorts of members: when a new edition is released the As want to shift to it, whereas the Bs want to stay with the old edition. Changing editions means that the As are burdening the Bs. Staying with it means that the Bs are burdening the As. Neither situation strikes me as inherently better than the other (and [MENTION=11300]Herremann the Wise[/MENTION] has explained how his group has reached a turn-and-turn-about compromise).
Now suppose that the new edition never comes out, because the game is "unified" around the old edition. Now the Bs have what they want, but presumably the As could be having a better time then they are - namely, if the new edition were released they could play that instead. Is this sort of burdening of the As by the Bs any less problematic simply because the As haven't yet had their preferences fully satisfied by the release of what is (for them) a better game? Are the As, in this situation, really enjoying "successful" play?
I guess it's possible that some players could be Cs - they are indifferent as to editions, but prefer the current edition - whatever it happens to be - over the previous edition - whatever it happens to be. In the "unification" scenario, the Cs are as happy as the Bs, but once a new edition is released, they jump ship and join with the As.
If the RPG market had comparatively few As, and lots of Cs, then I think [MENTION=85870]innerdude[/MENTION]'s point would be stronger, because releasing new editions really would destabilise what otherwise was successful roleplaying. But how many Cs are out there? And from my purely personal point of view, why should I think it's a good thing that game design is frozen just so that those who can't help being victims of marketing can be satisfied?