Measuring cooking ingredients by volume raises the question of packing density. How do Americans measure potatoes? Obviously not by the cup. Do they use some weird unit of volume like a bushel?
For small volumes of liquid it's more accurate to weigh, unless you have a narrow measuring jug. It's also easier to measure additively by weight. Most modern scales can be zeroed for each new ingredient.
I can't help suspecting that people who were educated before metrication may be more adept at mental arithmetic in consequence of having to perform calculations in a variety of imperial units.