You realize the difference between a company selling shares of itself, and a company that is running a securities exchange? The former could be a medium size lawn care service or computer shop for example, and might hire a lawyer and an accountant for a few hours each year, while the latter would need to be run by lawyers and bankers.
Its actually issuing shares and
selling them to the public which is most illegal. The mechanism is irrelevant. Exchanges are subject to regulation, but that's not really why GLBSE was shut down. Selling securities to just one person in the USA means you must register with the SEC.
I would say thats the typical US-Attitude of "We own the world." Nothing will happen when a US-Customer is buying shares in china. Or did you hear of plans for the next military intervention taking place in china? China has enough USD to make the US die, so no, nothing will happen here because of a bitcoin business. Most people doesnt even know what bitcoins are. Thats fetched way too far.
Its true that a company that was at an american stock exchange cant go out of it when only one single us-citizen owns a share from them but how will you prevent that someone is buying a share in china? Maybe i sell a share to an us-citizen. Is bitfountain forced to register with the sec in the us then? Not really.