Someone posted a chart of login data that they gleaned from the servers a while ago. It showed that there was a sharp increase (after an extended fall) in player logins during login campaign 1 that carried over to subsequent months. Even though it continued to drop, the average was still much higher than before login campaign 1.

This is just a crutch. It says a lot about a game's content/how fun it is when many people will not play it regularly, but will login/subscribe to get a cute costume.