To be further pedantic, milk also has a different specific heat which would overcorrect for the density difference by about the same amount.

The calorie is not an SI unit, it’s a cgs unit, and it isn’t coherent or order-of-ten with SI units.

Furthermore, I’m not aware of any market where you can buy energy in calories. Most will be in terms of Wh, mass, or volume, none of which would be coherent or order-of-ten with calories.

Except for food, I guess. But how much utility is there in knowing that you could almost pasteurize a liter of milk with a fun size snickers?