[kalleboo]

I've never understood why that is important?

Incorrectly wired outlets do occur even in the US, so it seems like it's safer to take that possibility into account and just design the whole system to allow them to be interchanged (e.g. make power switches open/close both lines)

[Symbiote]

> I've never understood why that is important?

On appliances with a physical on-off switch, it's best to have the switch as close as possible to the cable, and on the 'hot' side. If there's a fault (wire touching the metal case) then the appliance is still safe with the switch 'off'.

Nowadays, I think everything would have double-pole switches anyway.

[kps]

My experience of North American market consumer products is that they rarely have double-pole switches. A second pole would cost an extra half cent.