Don't know about semantics, but there is no big-difference in water pressure regulators and water pressure reducers as far as RV water systems are concerned. They function exactly the same. The pressure regulators sold at Walmart and Campo for RV water systems act the same as the pressure reducer that Entegra puts in there RV water system. Many vendors use the term regulator/reducer interchangeably.
Watts - A leading water pressure regulator manufacturer offers the following explanation:
" What is a water pressure regulator?"
"Also called water pressure reducing valves they are compact, inexpensive regulators that perform two functions: (1) they automatically reduce the high incoming water pressure from the water mains to provide a lower, more functional pressure for distribution in the home; (2) they "regulate" by maintaining a set pressure in the home usually 50 Ibs. thereby insuring that the home piping and appliances operate under a safe, more moderate, but satisfactory pressure. A pressure-reducing valve acts as a buffer between the high water pressure supply and the system or appliance. The mains water pressure is reduced to the safe required level during flow or non flow conditions."
The important thing is for folks to make sure to use one and occasionally assure the output pressure is regulated, even when water is not flowing. These devices have springs and can stop regulating. Safe Motoring