As a Czech who visited the US, I have to say this is absolutely true. Americans just smile a lot more. It's not that we Czechs are unhappy, but as the poster said, a smile is reserved for sincere interactions, not to people we've just met. I guess to a foreigner we all look like a bunch of resting bitch faces. But I think it's better than forcing yourself to fake a smile even if you feel unhappy.
“Milan, darling. Milan.”