Actually, you've got a point there Drtooth of the Mighty Film Corporation (lol).You know... the more I think about it, even if these things DID have functioning mechanisms that actually honked or dinged... would they be audible? Or how audible would they be? Would the microphones even pick them up as ambient noise, or would they just be so faded that they'd have to do ADR sound effects for it anyway?
I'm not sure about the Dingers, but I think if Honkers actually honked, they might be audible, but as you said, it probably would've been faded slightly. Keeping mind how loud those kinds of horns can get, lol.