Right now when you withdraw using BTC through bitstamp, you'll loose 5$ on every BTC.
So it is more profitable for mtgox to allow people to withdraw via BTC.
If they can't do withdrawals, we'll see that gox price will start moving upwards due to lack of arbitrage between gox and other exchanges.
I'd be afraid to hold money on mtgox right now.
I'm confused. Did you mean to say that if you sell the BTC and transfer out US from Bitstamp you lose $5? If you transfer 1 BTC from Bitstamp or transfer 1 BTC from Gox, you still have 1 BTC.