What value is gained for reading a book, watching a movie, listening to music or mounting a pretty painting on the wall? It's all entertainment. If he enjoyed doing it, that's all the gain *he* needs. Entertainment is an end unto itself. Fun and beauty ARE utility.
i'd rather do the other things i listed above than play WoW, but in the end, it's all fun and games.
When you do those others, you are culturing yourself and learning about the world and other people. All of those things (I would argue that this is a lot less true of movies than the others, though all the film majors out there would disagree) are highly educational and help you better yourself as a person. This is not true of video games, ESPECIALLY MMO time sinks. Saying playing WoW is comparable to reading is sad and says a lot about our society.
The first sign of maturity is the discovery that the volume knob also turns to the left.