no - you cannot use $250, must use Bitstamp quotes. see how the low prices hurt them? Again, this is all assuming MtGox is shutdown and goes into liquidation. If these low prices do in fact attract more deposits, then yes, low prices help and it is in fact a ponzi scheme.. like MfGlobal.
Ok, I will elaborate. Right now the sum of all fiat deposits and BTC deposits is fixed. With each trade a fraction of both becomes the possession of MtGox (trading fees, currency conversion fees; their profit). They must use their exchange to trade one into the other.
Now comes the hack, which reduces their profits on the BTC side, likely going negative. Now they have to balance this by exchanging their fiat profits for BTC on their own exchange.