It seems to me that the most common general use of these units is to describe ambient outdoor temperatures, and while I admit that I haven't traveled widely, I'

It seems to me that the most common general use of these units is to describe ambient outdoor temperatures, and while I admit that I haven't traveled widely, I'd be astonished to discover that most countries outside the US have physical environments more reminiscent of, say, Mercury or Venus, than what we in the US parochially consider to be Earth's standard range of atmospheric temperatures. I suppose that's why I consider Fahrenheit to be a very appropriate scale - since it centers nicely on the range of temperatures one might actually experience on Earth, naively assuming that America is representative of the rest of the planet - and isn't quite so arbitrary as one indexed to the temperature of boiling water, a phenomenon which a person in America - and, presumptuously, the rest of the Earth - isn't likely to encounter without having intentionally induced it. But perhaps -15 and 40 really are more sensible positions for roughly opposite extremes, and we really are the odd ones for using 0 and 100.