As No Prisoners No Mercy points out (in a post that first quotes me, then completely misinterprets what I said), both the monthly subscription model and the Free2Play model are based on "letting the other guy pay". In the monthly subscription model the players playing the least subsidize the heavier drain on resources of the players playing the most. In the Free2Play model the few percent of players spending money in the item shop finance the game for everybody else. Obviously neither model is fair.
Funnily enough, it is possible to play World of Warcraft with a business model which is extremely fair, in which every player pays proportionally to the cost and drain on resources he causes. You just need to move to China for that. The Chinese WoW business model is extremely simple: You buy a time-card with X hours on it, every hour costing around 5 cents, and every minute you are online is deducted from this amount of time you paid for. Nobody subsidizes another player, every player pays exactly what he is consuming, and the whole thing is fairest business model for MMORPGs possible.
Obviously it will be impossible to implement that business model in the western world. Nobody *wants* fair. "Letting the other guy pay" is a far more attractive business model. And whenever somebody points out the unfairness of it all, and how a pay-per-hour business model would be much better, he is shouted down with examples from ancient history, in which AOL charged people $9.95 per hour to play online games. That is of course completely irrelevant, a modern triple A MMORPG on a pay-per-hour business model would probably cost around 20 cents per hour to make the same profit as a $15 per month subscription fee. But as people arguing against pay-per-hour can hardly say that they are against fairness and for letting the other guy pay for them, they still use AOL as an example why "pay-per-hour doesn't work".
Nevertheless I have to wonder if we won't see a pay-per-hour MMORPG in the USA and Europe in a few years. As I described in the previous post, the "letting the other guy pay" business model leads to players moving to the game where they *aren't* the other guy. That leads to there being no other guy left to pay, which leads to games either shutting down, or changing the rules on who is paying.
Personally I would love a "pay 20 cents per hour" option for World of Warcraft. I do not have a constant interest in World of Warcraft, sometimes I play a lot, at other times I don't play for months. So I cancel my account when I burn out, and resubscribe later, which is a hassle. A pay-per-hour deal which would cost me roughly the same per year would be much more convenient, as I could stop and start playing without any administrative burden. But of course the people who profit the most from the unfairness of the monthly subscription model happen to be those that are also most active on game forums and blogs, and so a suggestion to make paying for WoW fairer will never be popular.