I think it's because the inspect is lazy or not smart enough to understand the issues of bonding and grounding.
It would be pretty rare for the H & C water piping systems not to be bonded together via a mixing valve in a bathroom or a faucet in at a laundry tub. As for the gas line it more tan likely will be bonded via the EGC of any appliance that has electricity run to it. I'm trying to think of a gas appliance that would not have electricity run to it and drawing a blank. Maybe a gas fired pool heater??
