- Flow of cheap btc starts to decrease the btc value of external market... Through arbitrage prices in Mtgox increases and settles above Mtgox's average cost of btc buy. (Caveat : Mtgox should not / cannot make customers withdraw more than 250 BTC)
- Prices find equilibrium and Mtgox purchase BTC in the external market for average $400 each... 750 BTC that is ...Deposits this back to itself...
Gox don't have an unlimited supply of actual BTC. No way they can "sell" enough elsewhere to equalise the markets without the public perception of Gox's liquidity changing.