Another thing to consider is WoW's breadth of content. There is a nearly bewildering array of quests, stories, combat alternatives, and Achievements to pursue -- not to mention the enjoyment of leveling up your character -- that the replayability factor is quite strong. Veteran players tend to focus mostly on end-game content, which is why each new expansion raises the level cap and offers more for the higher-end players to do. But it's important to remember that the path to Level 80 begins at Level 1, and it's been crafted in such a way that makes it easy and fun for new recruits to become immersed in the proceedings. This is something that many MMOs forget in their desire to compete: it's the low-level stuff that makes players stay, and is indicative of the kind of quest crafting that goes on at the higher levels. If low-level content isn't compelling, there's no reason to believe the high-level content will be any better.

What about the business model? World of Warcraft has been making a killing on the monthly fee setup, with no signs of either stopping nor changing the going rate. But the lasting trend among non-US MMOs is the free-to-play/microtransaction model. Is this something that can take purchase (so to speak) in America? Everyone loves getting something for free. And it's a great way to inflate player numbers: simply make your game free and people will sign up. But again, Blizzard invests their earnings into the game by constantly rebalancing, making sure the servers stay up and maintained, working on new expansions and in-game seasonal content ... it would be difficult to imagine WoW being made available for free, with the ability to pay a couple of dollars for a new hat for your character, or an in-game pet. Yet Free Realms seems to be picking up players at an astonishing rate; how many of those are former or current WoW players?

Let's also remember that playing other MMOs doesn't necessarily mean quitting WoW. When Age of Conan appeared on the scene, many players jumped on-board to check out the new thing, but kept their WoW accounts active, just as when Warhammer Online debuted. When players had had enough, they returned to their mainstay. At this point, so many have invested so much in Blizzard's timesink, it may take the actual closing of the game to make people stop playing it. For many, World of Warcraft is simply home base, and thus will always have a place in their lives. The only thing I can think of right off-hand that might supplant it? Worlds of Starcraft.