Almost positive that the amount lost with every transaction in the AF is 10% and not 5%. There is fee for both buyer and seller. In addition to things like repairs and teleportation(although optional), I can easily see how it would affect the economy in a detrimental way given the low rate at which Gil is generated post game.

Removing the fees from the AH and lowering/removing repair prices are quick fixes.

Also, to anyone talking about how the OP is wrong because you easily make money from the AH...go home, you're drunk and could not have missed the OP's point more.