True. Unless you encourage folks to pick up your models and flip it over, you can get by with just the stuff that can be seen from the side. Truss rods, brake cylinder, etc.
I brought home an AMS box car from NELSTS last night. Inspecting it on arrival the underside detail is over the top, They even model all the brake rigging EXCEPT on the trucks. My thought was if you are not going to model the connection to the truck brakes, then why bother with all the rods!