What does it seriously matter if the cities have few human players running around? We're all being anti-social just by playing this game, and that's what this is, a game. Garrisons are not expansion tied either, Blizzard can easily transfer your garrison to a new expansion if they want to, or to the old world, or wherever. They are here to stay though, in one form or another, I just hope I don't have to maintain two on the same character when the next expansion hits.