Analysts from the game industry have studiously addressed this issue from within, concerned as ever with providing their players with a superior experience. Even CCP, the most libertarian of developers, now engages in open war against the gold farmers. Since March 2009 (judging from Ajo's talk today), CCP has attacked RMT with a vengeance.
It makes sense. RMT is associated with degraded user experience (my original claim), credit card fraud, account hacking, and excessive CPU/user metrics. Playing the game for reasons other than game play are destructive. It harms other users. There's a good ground in policy for regulating RMT, and I am glad that CCP, with the Flak-88 of statistical power it now commands, has turned it reticule on this nasty problem.