[lifty]

My point exactly. I guess my explanation is lacking, but what I meant when I said that the exchange would be left with a deficit in bitcoins, is that they would not be able to create more "real" bitcoins, than there were initially deposited by its users. It's a zero sum game(if you ignore the fees).

But, that does not mean that MtGox could not create "fake" bitcoins inside their system, and extract their value by selling real bitcoins from the bitcoin pool that the users contributed to. For such a thing to pass under the radar, MtGox would need to keep enough real bitcoins in the system to satisfy the bitcoin liquidity the exchange needs. That would not qualify that much as an exchange anymore, but it would be more similar to a ponzi scheme.