Just a lot more fiat at Bitstamp. In theory, Bitstamp should be able to climb to 1,300$, but they will probably follow Gox.
Excuse me? On Gox's order book you have more than double the amount of fiat compared to Bitstamp's order book.
Compared with the situation a week ago, Bitstamp has a lot more fiat now. That allowed it to climb 120$ higher than the theoretical peak.