Austrian here, we are somewhat in between Russians and Americans, when it comes to smiling. But what I can tell you is that life is just so much better when people smile at you, even if it might not be a hundred percent genuine. My comparison stems from having worked with both Russians and Americans. Being around grumpy Russians all day long makes live really miserable.
I can't second this. Everytime I'm in the US I'm scared of all the friendly, smiling people, asking "How are you?" in such a friendly tone, it's delightful. Of course it's faked, anyone knows, and dare if you'd reply with "not good, my aunt just died". Awkward situation ensues, everybody tries to get out of the situation ("and what would you like to have for breakfast tomorrow?"). Now replay the same situation in ano…
All cultures have context clues. Your surgeon might have just met you, but be legitimately concerned about your condition. Your best friend might be interested in your emotional state. The stranger on the street might merely be "polite", or hoping/wishing you are having a good day, but neither wanting to hear a full dissertation on your emotional state, nor a recitation of your medical history that a doctor might find relevant.