I'm expecting the next note from MtGox to read something along the lines of "Thank you everyone for your patience while we drove down the market price. Thank you also for selling so cheap, we are now able to process withdrawls because we bought so cheaply on bitstamp. Again thank you and sorry we forgot the lube, but at least we only put in the tip this time."
They buy cheaply on MtGox. Bitstamp is pricey. So they 1) reduce the number of their BTC liabilities 2) cover the remaining liabilities with cheap coins.