Which is a surprisingly good approximation for how people feel. 0-100 is pretty survivable, with the mid ranges being most comfortable, and things outside of that range starting to pose serious threats.
50F (or 40-60F) is not the most comfortable for...well, anyone i think. Thats pretty chilly for most people, with 60F being the low side of comfortable (both inside and outside). Most universally comfortable temperature range is probably around 70-80F, which is not really "around the middle" in that 0-100 range. 70F is ideal inside temperature, 80F is a nice warm summer day outside.
75% is a C which is average for school grades, and a 7/10 is widely considered an average score for things like movies. 70-75F being the average room temp is pretty intuitive when used alongside other common scales.
Well, if the average American views 7/10 as the average on a 1-10 scale, it really just proves that their view is skewed, objectively incorrect, and cannot be used as a useful measure in this. Being wrong in multiple (and completely unrelated) instances does not make any of them correct.
I mean I never said it wasn't stupid, just that it's intuitive for Americans. 5/10 should be average.
But I'm not even sure that's purely an American thing. Go to a rating website like IMDB or MyAnimeList, 7/10 is considered average. I'm genuinely surprised that you're surprised by this.