Also, I was wondering why they had allowed trading, even after finding the issues with their systems - but that document made everything clear.

If they would shut down immediately, they would own:

  744,408 BTC is 367,704,753 USD... (at $493 per BTC).

But based on linked document:

  744,408 BTC (MtGox av price 160 USD= 119,105,280 USD)

Brilliant move.