I think they've lost a bundle today following Bitstamp's generally lower and super volatile rates. It surprising how little volume can greatly affect the entire market!
They charge 1% on every buy & sell -- so I don't think they're losing money.
Yes, but Bitstamp is very dynamic. I guess they just maintain balances with Bitstamp now and their USD balance went down close to $0, but maybe later they or their customers sold coins, which restored the USD balance. With this volatility, I've seen jumps of 5% up and down in seconds.