Suppose I gamble my life savings, buy Kleenex shares. Tomorrow a report comes out showing that using paper tissues causes allergies and prolongs colds. The shares tank ... I'd like a rollback please!
Strangely enough the guy that saw the report first and shorted those shares making millions doesn't want a rollback.
Of course he wants to keep the money, he traded correctly on what was apparently a correctly operating exchange and won. That's how this sort of gambling works.
MtGox screwed up. Why would they allow a transaction that crashed the exchange so easily?
People on the Mt.Gox forums are sceptical because the amount traded appears to be equal to the entire Mt.Gox trading volume (from the little I've read).
The speculation is that it is either Mt.Gox himself/themselves, an account representing the entire volume of all Mt.Gox traders or some other buyer who has been in from the start and has somehow escaped the notice of the other traders (this last option also accounts for the ability to break in as the account security apparently was very weak and hasn't been forcedly enhanced).
I'd say the confidence is pretty shaken up because the exchange has been hacked.
I expect from my bank that they give me back my money if it is being stolen from me, why would I not expect it from MtGox (if it is within their power). Banks routinely roll back fraud transactions and nobody complains - except the fraudsters, of course.
That's different: the bank would take a loss to pay you back, even if it couldn't recover the funds from the thief. MtGox isn't proposing to take any losses, as far as I've heard.
It sounds to me, as the first commentator on bitcoin.org says, that someone would like to keep their fat booty.