That must be a regional preference. I don't know anyone that isn't a big institution that has a backup generator powered by diesel (and definitely not gasoline

That must be a regional preference. I don't know anyone that isn't a big institution that has a backup generator powered by diesel (and definitely not gasoline). Permanently installed home backup generators are invariably natural gas or propane. Gasoline is a terrible choice in any case, it goes bad quickly if you don't stabilize it. The only time I ever see gasoline being used it's with little portable generators. Even then, I see a lot of people starting to choose propane instead now.