Is bitcoin's value dropping because of the halt of withdrawals at Mt. Gox? If so, does that mean the $600 range and most btc growth is dependent on the performance of the top exchanges? Where would btc be if we lost all the main exchanges?
It is hard to say 100% the exact reasons of price increases or decreases. Generally it is a number of factors. However the recent price drop is more likely caused by not being able to get BTC out of Mt Gox, so everyone on Mt Gox was selling to at least be able to get Fiat out.