PRVs, back flow preventers and expansion tanks for water heaters are not used around here. Typical city pressure is 50 to 80 PSI depending on where you are at in the town. The only back flow preventers are on fire sprinkler connections to the city supply and on industrial supply connections, but not on the typical domestic water connection. All outside faucets are required to have vacuum breakers. The city does have some PRVs in their distribution system to account for the elevation changes across the city. Around 100' from highest to lowest. As I recall that is about 0.433 PSI per foot, so around 43 PSI for the elevation change.
A town about 15 miles away probably requires PRVs in some parts of the town as there are places where the pressure at a fire hydrant is around 115 PSI.