closed by who? if it's not by their local jurisdiction, they cannot be closed by america if you think so, they are out of the law of america
Actually, if you're utilizing a ".com" domain, you're under the jurisdiction of the United States. No matter where you're based.
Just ask Kim DotCom who woke up one morning only to find dozens of US FBI personnel descending from helicopters onto his front lawn (IN NEW ZEALAND) kicking in his doors, seizing his property, businesses and bank accounts... due to internet piracy.
All of this just because his website MegaUpload had a .com at the end of it. Hence why his new website Mega.nz utilizes the .nz extension, thus removing it from the Jurisdiction of the united states.
So yes, each and every one of the aforementioned exchanges are under the jurisdiction of the united states - and if it ever becomes necessary, the owners of these platforms might wake up one day to find their wives and kids hogtied in the living room at the hands of the FBI