b) The PokerStars model. ACTIVELY exclude US residents, citizens, and entities from either listing or trading. Simply having a checkbox "I am not a US resident" is likely not sufficient, just ask the foreign online poker sites that the DOJ took down (servers, companies, and bank accounts all in non-US soil and the DOJ got sufficient help from governments where the activity was legal to seize assets in excess of >$500 million).
The implication of what you posted is that Pokerstars DID have a check-box for people to tick saying they weren't in the US. That's totally wrong. At the time the US moved against them Stars (and Fulltilt) both accepted US players and claimed they'd been advised that was fine. The actual action against them didn't hinge on them having US players anyway - but on the means by which funds were being transferred between US players and the sites (and the steps that were being taken to disguise those movements of funds).
I DO agree with the main thrust of your post - that claiming it's just a game won't have any impact at all on what does/doesn't happen. To have any chance of claiming something's a game (as, for instance, is the case with companies in Eve-Online) it would need to have no interaction at all with fiat-money.
All the time an exchange lists securities which claim to have a face value fixed in USD I really can't see the "it's a game" idea having a leg to stand on. Same for any listing which claims to give rights to the profits of a company conducting fiat-denominated business or having fiat-denominated expenditure/income (which indicates that company/individual considers fiat/BTC to be interchangable).
The main defence exchanges have had to date is being too small to matter and trying to avoid listing scams. Both of those things are ceasing to be the case - I'm amazed, for example, that no investor in Ziggap appears to have filed a complaint with the SEC to get the clown who ran it in trouble.