offgrid, good point. There are even more switches. That thermostat box, light tan on mine and about 2"x3", with a round thingy (a legal term, not an engineering term) has even more switching function since it turns the heating system off and on by temperature. How do you adjust it since there's no dial or digital readout?
Re the NEC, yes, some of it's there to prevent people from sticking their tongues on a frozen lamp post.
To use an over used cliché, at the end of the day, the users manual should adequately explain the switching systems for the hot water heater and it doesn't. Strictly speaking, the rocker switch on the water heater and the breaker should be enough, but only if they were well explained and the user was advised that the electric and gas functions are as different as a ......[I was going to put in some names of political parties, but out of respect for our very wise no politics policy] ....fish and a house cat.