I should have been clearer in my reply, because it sounds as if I disagree with xyzyxx, but I agree with this. However, "America's beer" is unusual. It seems to imply that America has only one beer (just as we have only one army, one president, and one flag). This is hardly the case. I suspect that if anyone uses the expression "America's beer" it will be in advertising. "Drink Blotto, America's beer!" This would imply that Blotto was the one and only beer "real Americans" like. It would be more likely for an advertiser to call it "America's favorite beer!"I would think "American" can refer to anything that comes from America or lives in America.
When I think of "America's", the only thing I could think of where it would be used is for things that belong to the country (i.e. to the government) - America's army, America's President, America's flag. But "American" could still be used with all of those.
I guess I should avoid saying "American XXX", which is a foreign brand. Thanks."America's car" would not just imply "a car that's very popular in America," but "far and away the most popular car in America." There is no such thing, although Chevrolet tried to position themselves that way for many years with their ads talking about "baseball, hot dogs, apple pie, and Chevrolet."
You can start an argument in most bars in the US by claiming that Toyota is "an American car." There is a great deal of controversy over whether we should say that about a car that is assembled here but sold by a Japanese company; it's more a political question than a language question, believe it or not.