Certainly. but as the market grows and more games become available free to play, and consumers become more savvy about it, I think it will steady out in some fashion. I don't think it's good business to fuck people over unless they are sufficiently invested, which takes a lot of time. Diablo 3 being the outlier, since people are already invested from Diablo 2, so Blizzard can prolly get away with hella shit at the moment.
Also I wonder how long Wargaming.net (World of tanks/battleships/warplanes) are going to run uncontested in their particular area. Ubisoft could do a mean Silent Hunter game if they wanted to, I think. And Ubisoft always tries to go hard in the paint when it comes to getting paper.
And ultimately I don't really think this business model will eat into conventional $60 discs or $15/20 download games. This seems far more likely to supplant MMOs, what with the various MOBA games (which are very social games though in a much more intense way than conventional MMOs) having absurd user bases that are incredibly invested.