In addition to what petit_robert pointed out about the Mt. Gox theft being orders of magnitude larger, you're assuming the densest available US currency and that it's conveniently pre-packaged for easy shipment.
What we're actually talking about, however, is like being able to teleport into a bank anywhere in the world, wave a magic wand which converts everything on the premises into tightly packaged $100 bills, and teleporting back out of the country. In the real world, running out the door with a bunch of duffel bags and people shouting tends to attract a lot of attention and make escape a lot harder than closing a network connection.
I fail to see how 99% of USD, which are just records in a database, is different than bitcoins in that regard then. The failure I would argue is in the original analogy of taking physical money to begin with.
Because electronic money transactions are reversible. If you can convince the right people that a transaction was illegitimate, it can be reversed and you can be made whole.
What we're actually talking about, however, is like being able to teleport into a bank anywhere in the world, wave a magic wand which converts everything on the premises into tightly packaged $100 bills, and teleporting back out of the country. In the real world, running out the door with a bunch of duffel bags and people shouting tends to attract a lot of attention and make escape a lot harder than closing a network connection.