> Luckily, everyone with deposits in Mt.Gox can convert them to bitcoins and send them to some other address.

If you have US dollars on Mt.Gox, and no one can take US dollars out of Mt.Gox now and there is very low confidence that this will change in the future, its going to be very hard to find anyone give up any other currency or virtual currency for US dollars -- whether you want bitcoins, yen, slips of latinum, or triganic pu, no one is going to give you them for dollars on Mt.Gox if dollars deposited on Mt.Gox are trapped.