Ive been playing Everquest 2 for awhile, end game wise you'll never lack a party and the community is top notch, however, when i rolled a new character it was shocking. It was like a single player game im paying a subscription on. This leads me to the next point of sustainability from a financial point of view.

If games that are top end heavy (majority of players end game) such as Everquest 2 is then ultimately those players get bored once they have completed it all and cancel subscriptions until the next expansion or what have you. So we have a situation where the new players feel like the games dead and old players going inactive for large stretches of time.

Its not all doom and gloom, after all Everquest 1 and 2 have been around for awhile and hopefully will be for awhile more, but the inability to pull in new players cant help the situation.