They really can not go for another expansion and still expect to get new players to fork up for old expansions, price for anything but the latest expansion needs to be symbolic if they want to keep attracting new players. Even for returning players some might think a few times if they are more than 1 expansions behind and have to fork up for old expansions they will just level thru and not even bother doing dungeons or raids in.

In good ol EverQuest you get original game aswell as all previous expansions (on exansion 17 atm) when you buy the latest expansion, not that they have a influx of new players but they do have some that come back to try it out.