Mt. Gox is a commercial firm run by individuals.  They can set any policy they like, and we can use other services like Bitfloor.

I'd like to see more pools of arbitrageurs who hold balances of cash and Bitcoin on each of the major exchanges and simultaneously buy where the price is relatively low and sell where the price is relatively high.

In faaact... once the JOBS Act rules are published, I wonder if we could crowdfund this.