Sounds like your impression is that Americans underdress compared to France, and golergka's impression is that Americans overdress compared to some other culture.
A lot of people moving here from France lately. They really stand out in their clothing habits :)
But who am I kidding with this injured pride, french really dress really damn well.
Having worked in a similar hot place (but probably not as dry) I can say the tolerance is smaller on 'mild temperature' places