Other MMOs have raiding, in fact so many of them do. Let Arenanet add a different way of doing things, so those who like raiding can pick one game and those who want something different can pick GW2. Also a good thing is if you do like the raiding type play style but also like the way GW2 handles things, and you can adequately divide your time between two MMOs then you can get the best of both worlds.