Different circuits in a single American household use different phases, I think.

Correct. Fun times trying to figure out why your power-line networking doesn't work.

The heavy load stuff is 240V anyway.

So it's the same way we do it in Europe with single phase, but I think it's easier to split three phases between single phase loads (most AC loads in a hosehold), rather than three phases between two phase loads (a few AC loads in a household). I still like the 120V plug connector with a key on the hot wire. In Europe I always wire the hot on the right hand side of the Schuko socket, as most standards have it on the right.

American outlets and plugs are barely usable. They go live even when you don't completely plug them in, yet.

The British plug is a pretty decent design from an electrical safety point of view. (However, they turn into caltrops in the dark.)

> The British plug is a pretty decent design from an electrical safety point of view

It's needlessly huge. I like type J (SN 441011, Swiss plug) and type N (IEC 60906-1, South Africa).

Yes, both of those would also work.

It's just that the American plugs are really the worst. See also https://www.youtube.com/watch?v=K_q-xnYRugQ for other badness.