Blizzard nerfs some of the top gold farming spots in-game which henders people from farming gold to use on the GAH, thus driving the player to use the RMAH where it can garner its transaction fee's.
Additionally, gold is not available to purchase on the RMAH which if it was would allow players to have a single transaction fee to purchase a large sum of gold to use on the GAH for multiple transactions. (If Blizzard allows this, they lose out on multiple transaction fee's).
Would I mind if the developer created items to sell on the RMAH? No, but as in other games that are F2P, the store (in Blizzard's case, the RMAH) listed developer made items.
It might be a reach, but maybe the FTC or some state's AG needs to make an inquiry to the legitmacy of the RMAH and who is behind each auction.