MTGOX is not a bank is a exchange
Over a year ago, Mt. Gox started to support BTC exchange markets in addition to BTC/USD.
If on the BTC/CAD market they were to only show the actual bids and asks just for buying and selling bitcoins with CAD, the depth would be real low and prices would be horrible for buying in any size.
But look ... it has depth -- about as good at BTC/USD or any other currency market at Mt. Gox.
- http://bitcoincharts.com/markets/mtgoxCAD_depth.html
So what that depth includes are bids and asks from other markets at Mt. Gox, after adjusting for some fee amount to convert those funds to CAD.
So Mt. Gox doesn't maintain CADs for each sell into a BTC/CAD bid. Sometimes they need to then convert USDs or EURs or whatever other currency into CADs to serve your withdrawal request.
From another thread:
Q.) Does [MtGox] maintain full reserve? (i.e., [MtGox] controls bank accounts with all customer USD funds and controls wallets with 100% of BTC funds. None of these amounts loaned out.)
As described in our Terms of Service, customer funds are kept in full, and none are loaned.
As described in our Terms of Service, customer funds are kept in full, and none are loaned.
So though they do assert that they maintain all customer balances, the value of those funds may not be in the specific currency of which you are wishing to withdraw. So for each of your $1 CAD to be withdrawn Mt. Gox has $1 CAD worth of fiat, just not in CAD. They probably have an active forex account moving funds from the currency where they have excess inventory and filling in the currencies where inventory is low or out.
