After thinking about your question more, I'm still unsure, since Kerpupples allegedly said it was due to Bitcoin's tx-malleability issue, and not MtGox itself. Not sure about this one, good question.
Might want to check, but several months ago a story circulated with proof that fewer than ~200 BTC were ever stolen due to tx malleability. If this specifically was the claim Mark made, then it's a lie.