This is not the case. This part: "one milliliter of water occupies one cubic centimeter, weighs one gram" is known by most people, even kids in primary school. In other words everyone knows that a litre of water weighs one kilogram, and that there are 1000 litres in a square metre. I concede, though, that at least in Italy, which is the country where I was born and raised, most people wouldn't know the next part: "and requires one calorie of energy to heat up by one degree centigrade".
;)
We are taught to use the scales for measuring ingredients - and thanks to this trick you can weigh water (and milk) and vegetable oil (using 5-10% less) if you don't have a measuring jug.
They taught us that in 4th grade in cooking classes. Then they made us remember that in physics and chemistry classes 2 years later.
Of course I don't remember a lot of things from the 4th grade. This one stands out.
I wouldn’t be so certain about that. I’ve used that to conceptualize volumes and weights ever since I first learned that in school.
Probably a similar number of Americans know the same facts. And any of them would answer "How much energy does it take to boil a room-temperature gallon of water" in the only sensible way -- look up the conversion of gallons to liters, do the calculation in metric, and convert back from calories to whatever unit you want (BTUs, I guess).
The point is: nobody, including Americans, uses the customary system in chemistry labs. Nobody ever has cause to calculate how many BTUs it takes to boil a gallon of water without reference to the metric system. So the argument is a bit specious.