I agree with the "extremely American", but the not getting upset is just also an extremely American adoption of elite mannerisms at all levels of society. Publically showing emotion is considered vulgar and low-class in many cultures.
Kids learn really fast that they can't just act out with their peers for fear of rejection by the group. It's extremely strong and parents need to teach the other half of it, dealing with negative emotions WITHOUT acting out. I feel like DT does a disservice here.