Actually, my speculation is that Gox itself purchased coins, artificially crediting a cash number to a seller with plans to cover fiat withdrawals from their cash reserve if it came to that... though it often did not come to that since people withdraw coins more often than the burdensome fiat withdrawal process. I speculate that they did this to stimulate volatility - necessary for them to generate legitimate revenue. After enough time goes by, there is substantial Gox-backed fiat in user accounts - which originated solely from the earlier cash deposits Gox pulled commissions from (and gathered from pseudo-coin sales). Conversely, I speculated that Gox sold coins for the same reason, crediting investors btc balances with coin iou's. In their selling, they simply gather up and siphon off more of the original cash pool.

As Gox spends their cash reserves and fulfills withdrawals of promised coins, it is anything but a zero-sum game. This really is one of the foundations of my speculative conclusions.