The question is what will be the drop off be like after two months when the people that only came back to see the expansion. You saw spikes like these around all of the other expansions.
I do agree that GW2 is probably one of the strongest competitors to WOW at the moment. After seeing an MMO implement like one of the previous posters said, the tag-less mobs is hard not to want that in other games. The dynamic events that cycle through basic PVE quests to outdoor world boss is a fun change in that game.
There are few things that World of Warcraft seems to do a bit better such as tying the lore together a bit better. It is probably possible for the games to coexist.