OK, you've got a point, MTGox is a central point in a supposedly decentralized network. I think that problem has been recognized, however, and is in the process of being remedied.
Good we're on the same page!
But do you realize that the exchanges as a group CANNOT ever be forked from one another?
I'm not sure in what context you're using "forked." Don't we
want all the exchanges (into which group I include the people selling bitcoins for other currencies on #bitcoin-otc, SR, and other darknet sites) all using the same blockchain?
I don't understand this "forked" thing either. An exchange is essentially an independent entity. Some people put BTC in, some USD and others other currencies then they exchange and then cash out or exchange again as desired. They need to be hooked into the Bitcoin protocol and the banking system (the latter appearing to be the "hard" part of being an exchange, an indication that Bitcoin is a superior solution, by the way). But any interaction between them would typically be done by third parties by way of arbitrage.