Good idea, one of the most unlikely to work yet. How exactly do you 1) figure out who in the game is addicted, 2) approach them in a way that'll make them receptive to you, 3) figure out how to bill them afterwards? (OK, assuming that the last one can be skipped and the therapists are only doing this out of the kindness of their hearts, it's still the slightest bit of problem.)
Although I agree psychologists trying to cure people of WoW addiction would be more efficient if they played the game and understood it more. More power to Blizzard if they go through with giving them discounts.
(The idea of those doctors becoming addicted themselves, I find it even more unlikely, although still hilarious.)