I think some of this phenomenom is cultural and the rest can be owed to stupidity. In the US, everywhere is air conditioned, everywhere. So, Americans tend to be a bit more inclined to prefer cooler temperatures, even at night. While in Europe, air conditioning is not as common, nor necessary in many locations.

However, I completely agree that a hot cabin destroys the premium class product. On more than one occasion I have asked the crew to lower the temperature and they flatly refused. I had to get a CDC (Chef de Cabine for AF) involved once who insisted that TWENTY-FOUR was the recommended temperature. I had to politely disagree and insist it was lowered. I am a rather athletic man and am not prone to over-sweating, but when I wiped my face and neck with the tissue and showed the sweat to the CDC, she turned it down. If you don't like it cooler, you can always put another blanket or sweatshirt on. I can't always remove more clothing.