Some people claim that free-to-play MMOs are the way of the future. Others insist subscriptions offer the best entertainment and fairest playing field. To me, the whole argument is flawed. Neither F2P nor subscription games cost more than a trip to Subway each month. Real people just want to have fun and will pay for it if they get their money's worth.
The strongest argument for the relative success of F2P games is that while most subscription games since WoW have been a disappointment, F2P titles seem to have grown in stature and importance. But there's an interesting little trick there. The hugely successful games lately, while promoted as F2P, actually use just about every business model in the book, subscriptions included. Look at FreeRealms and Wizard 101, for example.
There is a single reason, larger than how people pay, to why the free-to-play games are finding some success while so many subscription games have met tough times.