Just like any other successful virtual world, what makes people an addict is fame. The game mechanics has nothing to do with why people play the game so much. They play it because they're well known, well liked, and powerful; three things they probably don't have in real life. In other words, playing WoW is escaping from the real world into another where everyone likes you, you have an easy time making friends, and girls will talk to you. If you think of all your friends addicted to the game, you will see how it is so hard for them to step away from this scene.