Other exchanges don't use Gox. They rely on their own order books. A trading engine uses the set of buy and sell orders in its database to execute trades. What happens on btc-e is independent of what happens on MtGox... except for arbitrage. The prices on the exchanges tend to agree over time because if there is a large discrepancy, people will buy a lot on the low exchange and sell (the same coins) on the high exchange, bringing the prices closer together. That being said, non-exchange traders do tend to rely on Gox a lot, but arbitrage guarantees the prices are never too different among the exchanges, so in my opinion in doesn't matter that much.