This happens whenever a new MMO comes out, or whenever there is, in general, a top ranking franchise on a market that almost dominates said market, and a new underdog pops up.
But this one in particular.
WoW finds more subscribers in its couch cushions that most other MMO’s even have. It is a very large fish, even in the growing pond that is the MMO market. It will be quite some time before it falls.
I never understood why people couldn’t like multiple things. GW2 seemed good in the beta, but I have a collectors edition key sitting unused on my desk because my friends wouldn’t stop going on about how much better it was than WoW. That, more than anything else, turned me off to playing it.