Even if Mtgox lost a large number of bitcoins, they can temporarily work like a fractional reserve bank until they recoup all the accounts with the 0.65% fee.
Gosh, it's like a bitcoiners dream!
"Chargebacks"
Fractional Reserves
Everything we stand for as a community!
Yee Haw cowboys.
What would you rather? Him to just take bitcoins away from everyone, possibly a large number. Or just pretend he still has them until he has replenished all the bitcoins with the fee? Just like a regular bank.