To a European, 40 degrees is fecking scorching. -10 is fecking cold. Europeans don't wander around wondering if it's really cold or not because they're not using the F scale. 40 to them means just what 105 would mean to you. The centigrade scale was invented to put temperatures in terms of water. 100 equals boiling, 0 equals freezing. I tend to convert all temperatures in my head to both C and F depending which one I get first. For a benchmark, 37 is body temperature.
As far as the distance- tens are much more sensible to work with. Anybody can count in tens, hundreds, thousands. Not quite as easy to multiply times 5,280 or 1,760 or 36 or twelve.
The US military uses metric for distance- because it's smarter. I try not to read a whole lot more into it than that.
You're never going to have to worry about losing the various scales of measure we use because it would be much too costly for the US to retool. You'll be able to go on using measures based upon how far a Roman soldier could march etc until you die. In the UK, they do you one better. They measure human weight in stone. I still don't how much I weigh in stone- probably never will.