Another reason is simply that Japanese houses are much smaller. My dorm is just old enough that the insulation has worn down and lets in a lot of cold air, but I think most houses and apartments in Japan generally do not have that problem.
Japan is a country that has some very different perspectives than the U.S., but it can be pretty easy to get used to as long as you try your best to respect and be a part of the culture and not act like the famed ignorant "American tourist."
