Lets be clear here. I am a huge WoW fan. I love the game and the challenges to both timing and thought that it presents. I am not a fan of paying every month to play it. I know that it represents a contribution and you can gain a ton of entertainment value for that dollar, but it can become obsessive.  Especially when you consider that a large portion of the gaming community do not get to spend everyday online. In fact, I would bet that a fairly large portion only play once or twice a week. Some would also only play a few times a month as time permits. If blizzard were to give this a go it might open up the game to a few more people that might never play otherwise.

Blizzard discuss making World of Warcraft free : PC Gamer.