Some info here: http://www.reddit.com/r/Bitcoin/comments/1z37zw/mt_gox_has_a...

"MtGox still has at least 200k BTC"

Here are the possibilities, as far as I can tell:

1) That information is inaccurate.

2) MtGox lost their private keys.

3) The private keys were kept in a bank vault, which was seized by a foreign entity like the US government at some earlier time.

4) MtGox stole the coins.

The management of MtGox knows which of these is correct, but they probably aren't going to say.