As the commenters over there say, there's a good reason for that, and it's because most of the economic play in WoW is completely optional. Aside from repair costs (which can be high for raiders, but for everyone else are fairly inconsequential), you don't really need money at all; given enough time, you can collect whatever you need from somewhere in the world, either by simply collecting ore or herbs, or by running instances and doing quests. But that doesn't mean that the "rent seeking" comparison isn't valid.
I cannot ever remember, though I'm sure it has happened at least once, hearing a complaint about a quest reward, or complaints directed right at Blizzard about auction house prices. Sure, there are complaints about those from time to time, but in general, players understand that the market in place there is a completely free one -- if you don't like what people are willing to pay for goods, then find something else to sell. Of course, the in-game economies of Azeroth aren't directly comparable to real-world markets ("Eaten by a Grue" makes another great point over in the comments there: that in-game items are essentially worthless to Blizzard, and therefore they are immune to corruption, another significant difference), but it's even interesting thinking about where the differences lie.