Wasn't The MTGox account in a us bank?
MtGox has / had a Dwolla account linked to a U.S. bank. They also have an account with a Japanese bank for all other funding methods. As far as I understand, it is irrelevant where the bank accounts are held. What pegs them as a money transmitter is holding U.S. customer funds and facilitating the exchange of USD for BTC and vice versa.
That's right. To put it technically, Mutum Sigilum was subject to US law because they were servicing US customers. They were an easy target for the enforcement of those laws, though, because they were US based and had a US bank account.