>I've never understood where 220 and 110 came from.

Those are the nominal or 'average' voltages. Nowhere has 100% consistent voltage supply. The UK goes from about 216v to 250v. If you were to plot the AC sine wave, the peaks would be nearer 330v RMS. But that variance is of no damn use to anyone who makes devices, or the consumers shopping for something compatible.

So a nominal is used, a nice easy number for everyone to read and go 'oh yeah, that works in my wall socket'.