I know a guy who's really, really into football. Watches hours of games every other night or so, has a "fantasy" team that he's constantly fretting over and checking online stats for, etc.

As far as I can tell, the only thing that distinguishes this obsession from a WoW habit is that more people like to watch football, so it's accepted.

People who get seriously addicted to WoW are usually either looking for any escape from reality, or they have the type of personality which tends to get addicted to something, whether it's online games, math puzzles, tracking railroad schedules, or whatever. There's no question that these people might act in unhealthy ways, but WoW is the symptom of their problems, not the cause.

(disclosure: I used to play WoW regularly)