The only thing selling to the US would accomplish is people from countries where it is available leaking and cracking the client. It's already been done many times for Minecraft for the people that can't afford it - but there have been plenty of people who used a pirated version as as a "trial" and then proceeded to purchase the game.
Mojang games would still get to the US, and plenty of people will still play them. The difference is that they wouldn't have a chance to make any money off of them from the people over here.
I've already got my Minecraft though and none of the other games interest me. I highly doubt they will create some amazing game that will take over Minecraft either. Truthfully, no game interests me enough anymore where I would even remotely consider pirating it. I just buy games that are available and play through them. If I can't have it, oh well. I'll play something else.
I'm not worried regardless. It's a stupid business move to stop selling to what is arguably the world's greatest consumer market for entertainment. That, and anyone who's going to do anything to make money, especially something like video games, should expect to get into legal battles regularly, over nonsensical stuff that probably wouldn't even make it to court.
But of course it also doesn't help that the media sort of throws it out there that "IF YOU DON'T LIKE SOMEONE, SUE THEM FOR ALL THEIR WORTH". That sort of mentality isn't helping anyone or anything.