WoW has critical mass going for it. Played it for a few years, leveled, raided, spent time with a few guilds. The big, huge difference between WoW and everyone else is the simple enormity of the player base. More people to group with, more chances to find a guild that suits you, more people dissecting the game and putting up sites with walk-throughs, specs, item lists, etc. All of that leads to a certain quality of game life that allows WoW to make money -in spite of- the game quality, not because of it. WoW was simply a good enough game that has remained good enough, that came at a time when it managed to catch an amazing chunk of the market, and it is that chunk alone that sustains it in spite of better games coming and going (though part of that is no one realizing that any 'WoW killer' game will still take -years- to actually do so.)