As soon as there's a slight drop on Gox, Bitstamp absolutely shits itself. But when there's a big rise then Bitstamp just doesnt care.
I wouldn't call a $1-2 drop shitting themselves. MtGox dropped by $2 dollars as well so fast and twitchy fingers on Bitstamp will sell immediately to make a quick buck. Besides it takes more fiat to drive up the price on Bitstamp than it takes bitcoins to drive the price down. Bid side is pretty thin close to the market price.