The current fee structure makes trading unprofitable when the system is as stable as it is. With that being the case less people will be actively trading. Forex trading has a fee structure that is built in to each trade where they basically skim from the money in between bids and asks when they match each order. It works because they have huge volumes. Clearly this is not the case on Gox with a 20k volume. The volumes are so low that it's hard to make a 'decent' profit, though they could pull in about 900k each year with the current (full) fee structure, 13.5 USD/BTC and a steady 20k volume each day.