I remember growing up, my dad used to BEAT my @$$, if I shown any type of anger on the court - not "classy" as he'd put it. I think it has to do in which you can't do that anymore in this country - the whole liberal anti child abuse laws and such. Or it could be that kids nowadays are weaned to be entitled to do whatever the hell they wanted. Doesn't matter it is what it is.
Well, I assure you that the "whole liberal anti child abuse laws and such" exists in Europa too. I really doubt that the parents of Federer or Nadal beat them to teach them to play tennis.
I think the question is not good from the beginning, because americans grow in the same type of society than the europeans, and they have the same kind of temper.
Querrey and Isner have already been named as couterexemple, but we could think of europeans players who have quiet a temper. Look at Ferdando Verdasco, Wawrinka, Berdych.