MtGox may comply with an order from a Japanese court, but based on the Bitcoinica experience they're not going to comply with orders of foreign courts unless they have assets located within the jurisdiction of those courts -which at this stage seems to be Japan and Poland.
Mt. Gox is complying with orders of the U.S. District Court in Seattle in the Coinbase case.
Mt. Gox has an explicit legal presence in the US, in Delaware. They established a dummy office so they could register with FinCen. That makes them subject to US courts.
There's so much trade between the US and Japan that the mechanisms for resolving contract disputes are all in place and well worked out. The Government of Japan even has offices in the US to help. That's part of what the Japan External Trade Organization does.