So the people more eager to buy did it even at 250 -or during the bull trap at 200-170. So now ther's scarcity of USD you could say...
There's scarcity of USD because everyone's USD is tied up in a frozen exchange where it takes 3-5 days to withdraw. (Compare to their bitcoins, which can easily be moved elsewhere to sell in 1-2 hours).
The $64,000 question is whether people are withdrawing that money right now, or waiting to buy when Gox comes online again.