Probably worth mentioning that if you could afford a SOM set, you were pretty well off and not exactly short of a few bob. Smaller generating sets were also sold by Lister and Petter, and others, but their cost to buy and run was way over most ordinary folks means.
The Lister CD 110V generating set that we have was one of a pair, installed in a large country home with battery banks and switchgear, probably part of a large estate to be able to afford that kind of plant.
Regarding America and the electrification of the country, it would have happened anyway, just that war probably accelerated its implementation.
England and Europe are far easier to electrify as they are very compacted and close-knit. 700+ miles and you have driven top to bottom in England, we did that driving Indiana to PA, across Ohio state the other year, and that's a small part of the total, coast to coast.
Peter