I think it is somewhat important, as it can indicate how much long term support and additional content there will be for the game. MMOs have a life of their own, but if you know the game you are playing is being played by many others, you know it will go on. Terminally ill games that have few players will end up going away. That is frustrating when you invest the time over months/years then poof....gotta go somewhere else and do it all over again. Having confidence that the game will endure is important.