Steve, prior to the depression, even here in the US voltage and frequency differed by area. In Chicago, there are still sky-scrapers that have only DC!
Apart from just pure chance, some places deliberately chose power different from their neighbors. Our Irish member, "djk," has expressed wonder that Ireland didn't adopt shamrock-shaped plugs, 120 volts, and 72.5hz- just to make thing harder for visiting Brits!
There was also a lack of "standard plug patterns" even here in to the '70's. Indeed, RV parks still use a "non-NEMA" plug.
