Its interesting with WOW, I dont think its so much that there is an addiction to the game, but something else. I think the addiction is the social aspect of the game, same as people have addiction to the social networking sites.
There are a heap of sites that talk about WOW addiction, just search google with WOW addiction. Its why its so heavily targetted by the media when discussing games and their claims of addiction. Of course when you have 10million users some are going to have problems.