What the relic questline can give though, is longevity. At the moment, there really is no incentive to stay subscribed from one patch to the next, since each major update completely antiquates gear 2 generations ago. It's a great business model for the casual player to pick up and play and then just drop, but outside of crafting and relics, you could drop the game and catch up pretty easily several patches down the line.
Long questlines generate constant and secure revenue with the players that remain invested in the game. Take that away, and success rests solely on how well you can craft each update. It doesn't have to be the entirety of the game, but a smart on-line game (or any game) is designed so that you have instant, mid, and long term goals for the player to keep busy with.
