You have to be careful when comparing the US to the rest of the world, because the US is the one breaking the ground of new levels of relatively-well-distributed wealth. (Put aside the question of how well for a moment, please.) For instance, it turns out that the US did not have uniquely bad dietary habits around flour and sugar, it's just that the US was the first to discover people really like to eat that crap and could afford the infrastructure to deploy it; now the bad diets and the consequences are spreading like wildfire as the requisite level of wealth is spreading. (dhughes says Canada is there too, certainly they have that level of wealth too.)
Correspondingly, it is hard to know whether the rest of the world cooks their own meals and don't eat out much because of some sort of intrinsic betterness or culture, or because they simply can't afford it yet. Once people can afford it in more places they may be more inclined to eat out. And if they do, they'll start losing the ability to cook overall. Culture may induce some lag but there's no particularly compelling reason to think that more countries won't follow along.