Yeah, but there's no need to leave your money with the exchange once you've changed currencies. The problem with MtGox was that someone was effectively using it

Yeah, but there's no need to leave your money with the exchange once you've changed currencies. The problem with MtGox was that someone was effectively using it as their wallet... probably for convenience, but frankly, it's not that hard to add/remove BTC from your exchange account so as to not take extra risk and leave it available for a hacker or snooper to take.