Unfortunately, many novice bitcoin owners will choose to sell their BTC at MtGOX because (a) it seems to offer the best price, by far; and (b) it is still cited in the news, blogs, and chart sites as one of the main exchanges.
read more carefully. Many would-be arbitragers have sent bitcoin to gox, but nobody would send or is sending USD or fiat to Gox. All it takes is ONE arbitrager to drain the entire fiat account totals left on Gox by selling bitcoin there, transferring the fiat to another exchange, buying bitcoin on the other exchange at lower prices, transferring the bitcoin back to Gox to sell at higher prices, rinse and repeat. Everyone including me is buying bitcoin at whatever price we can get to transfer to another exchange and sell there to cut our losses.