

I’m guessing a tankless water heater involves some electronic controls. It probably could be designed to use low-voltage DC with a battery backup, but that would be fancy.
A gas stove should never need electricity for a burner to work if the user supplies another source of ignition like a match. This is surely a “safety feature” to prevent people from leaving the gas on when the electronic ignition is unavailable, but nobody with half a brain and a sense of smell would do that.
Companies that were app-first like mobile games probably won’t cut prices much if any. Companies that were web-first like Proton and Patreon probably will.