(It's as if the US grid characteristics were decided by the copper vendors... ;-)
It was designed without an issue with copper usage. Europe had very little development and quit a bit of rationing while building out the grid post-WW2. The US had no such issue and spent no time working within those constraints.
In your case, I believe each prong of your two-prong plug gets a different phase, so you have 3 possible pairs of phases to power each circuit from. This has the advantage of requiring smaller wires, but the disadvantage of increasing the risk if one is electrocuted.
Avoiding this was one of the design parameters of the "Schucho" plug design that is reasonably standard across Europe. You'll note the three prong plug has a longer ground that makes a connection before any hot one does. The US three prong is supposed to work that way too but the ground pin isn't long enough.
I continue to be amazed how many devices still ship with only two prong plugs (everywhere: Europe, North America, Australia...) even if those prongs are polarized.
Because most devices these days have plastic cases (Class II double insulated), so there's nothing metal to touch to get shocked even in the case of a fault. That coupled with how GFCI/RCDs are being widely adopted as well leads to grounding not being as important.
Meanwhile I'm sitting 2 feet away from a nearly completely metal lamp with a two-prong plug.
The US is 120V, or split-phase 240 V. Depending where you are, it's allowed to be ±5% at the meter. NEC guidelines say no more than 3% voltage drop from there.