but mtgox is the leading exchange, when price moves on gox others follow, price cannot completely crash on other bitcoin exchanges till gox lets market move again, the selling you see in the other sites is minor, just people willing to take loss, so that in the event of gox continued selling into the unknown they are not trapped.
So your contention is that if Mt. Gox is down, people who would otherwise panic sell won't just panic move-to-another-exchange-and-sell? Who in their right mind, believing that the price is going down, would not sell just because their favorite exchange is closed?