At my house in my room it is neither 110 nor 120, it was 115.6V the last time I measured it
I wonder if the difference between 240 and 120 in the house would make a big difference in efficiency? It does definitely mean you can use thinner wires for the same current in house wiring, but on the same hand the insulation is thicker, and modern electronics, which usually runs at low voltages has to work a bit more to step the voltage down.
You can also ask why power in the US is at 60Hz, while some places run at 50Hz, or possibly even more different.