Assuming the person(s) placing that ask wall don't:
(1) Have special relationship that allows them to withdraw for some additional fee.
(2) Have insider information of an upcoming partnership announcement that resolves all withdrawal issues.
They may still just be betting that the price will fall. They can then re-purchase those bitcoins on Mt Gox at a lower price.
Thus far, that hasn't been working out well for them.
nah, I think its pretty plain and simple: someone is willing to take the risks and just sell.
or it could be gox selling their btc stashes at premium prices.