The largest exchange not being on US Soil is bad for the Government. What's not in the US can't be controlled.
Unfortunately, that's no longer true, thanks to Mutual Legal Assistance Treaties. Here's the one between the U.S. and Japan:
http://www.mofa.go.jp/region/n-america/us/treaty0308.htmlI'm not implying that the U.S. will pursue Gox in Japan for failure to register with FinCen, but the mechanism is in place should they choose to.
As in controlling Bitcoin. Stoping it from becoming the dominant world currency. If the dollar stops being the world reserve currency, the US is screwed. No more printing money to pay for wars!