World of Warcraft is widely considered to be a highly refined Skinner box. If you're unfamiliar with the experiment, I strongly recommend that you look it up on Wikipedia and then google "wow detox". Also, you may want to research Asian governments' restrictions on XP/hour.
Yes, i'm aware of all this, but internet can also be considered like that, and also, many entertainment. And wow is just a game among many, i don't quite agree with this generalization.
You can't judge a medium for what is done with it, but for what you CAN do with it.
I'm sure you'll come to the right conclusions.