THe msq is written with one WOL in mind, sure, but the game itself is still a MMO with a community/multiplayer aspect. Even with trusts you can't get through all of the msq without partying with other players in trials, and of course duties beyond the msq are all multiplayer. The story may be written like a single player game but it's still very much a MMO, not just a single player game with a tacked on multiplayer mode or something.