Just because they aren't in the US does not make them immune. Immune from criminal prosecution, yes. But if a civil suit against them was successful, they could have any funds or assets in the US frozen and companies that do business with them could be sanctioned which would hurt them pretty bad.

Regarding extortion, under US law forcing another to do something against their will or face repercussions is called coercion which is codified under extortion. I would not have to prove this in a court of law as I am not suing them. But I do intend to file a formal complaint with the Attorney General of my state and with the emails they have sent me repeatedly asking for my personal ID for my $100, that is enough to get the formal complaint to stick with extortion in the record.

It is my hope that others will do the same so that in the future, in the event of a more broad act of malfeasance on the part of MtGox, a civil case will be much easier on the side of the consumer.