I believe that some broad statements are getting made. As far as Suburban, they make several models of water heaters. They also make models that do have an inside switch for the electric heating element. It utilizes a 12 volt switch and relay to turn on the heating element.
Just ask Turbs, his RV came from Forest River with a factory installed Suburban water heater with an inside switch on his panel for the DSI and another one for the electric heating element.
I'm sure there are reasons that FR Inc uses the differing models of Suburbans on different RV's as well as Atwoods, and Girard. It may be a division by division choice.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.