While I am only sitting on about 2g (and have a long way till I hit 30k, I have found that my main motivation to play the ah has been more anxiety driven rather then to extend my sexy epeen.
I don't want to ever hit a road block in this game caused by not having gold. For example, on my first toon, after about a week playing, I identified that the lvl 30 mount needed a (relativly) large amount of gold. So I needed to make gold, the research I did pointed me in the direction of the AH and I have never looked back.
Plus, as the AH is the best form of PvP in the game, my sociopathic side gets a real kick out of undercutting blue gems by 1 copper