I thinks its because the addresses are only able to link to your real self once you make a link. (buy something and have it shipped to your address, deposit real money with a exchange that requires your identity, etc..)

however you could always make a new account on mtgox, send the coins to the exchange and send them out to another address you made, and I think, unless the exchange gives that transaction (That is internal to their network) to the authorities, you can begin to remove your-self from being traced.

The way I see it is this, you can determine how traceable you are in Bitcoins, you can't determine easily how traceable you are with native transactions (USD, AUD, EURO, etc...) This may help you hide better