The buyers are high risk players who have accepted taking a risk and are gambling with money they can afford to lose.
That's me - I've written down the cost of MtGoxBTC/USD to zero, but continue to buy MtGoxBTC.
Getting back cents on the USD if it goes bankrupt is of no interest to me.
Ah yes I forgot another thing:
The price point where people decide that an x% chance of receiving X amount of btc is more attractive than a y% chance of conducting/winning a lawsuit and receiving Y amount of btc, and people who don't think that a lawsuit is going to work or that they would ever receive USD and have a better chance of receiving BTC, despite what the lawyers say.