Feisty aren't we? The reason why WoW is still dominating is because of it's age. The game was released just when MMOs started gaining a lot of popularity and it was really the most bug/cheat free MMO at the time. Before that it was mostly FPSs and whatever else the market had to sell as it wasn't really as big as it is now.
The market is hungry for something else. You can't expect MMOs to grow and grow when people have less and less free time for fun. Games have become a source of instant fun so really leveling characters untill your eyes bleed and gearing them up isn't cutting it anymore. People want fun when they pay for it and can't afford to sit behind computers for 5hrs+ a day just so they can get to the best part of the game.