That's definitely not true. McDonald's and Burger King were both markedly worse in my experience. A shame in-n-out isn't abroad, and haven't found a Taco Bell or Wendy's yet. Not that I would really go out of my way to eat fast food overseas now that I'm an adult... I don't even eat these things in the US.

There's wide variability within the US anyway. I've noticed that affluent suburbs tend to have great fast food, while urban and rural environments have awful fast food.