I wonder if events on the int’l stage play a role as well. During the credit crisis, the dollar enjoyed a period of surprising strength versus other currencies, as people rushed into the relatively safer currency. I noticed around the time that virtual currencies were tanking vs. the dollar, and perhaps some of the effect could be due to the “flight toward safety”. To test this I guess you would have to control for currency printing in-game (via gold farming or gold dumping by the developers).

I suspect that currency management by the developers could be the stronger cause. But how to test for the volume and velocity of WoW gold in circulation…