During our years of travel we have seen people drive off with the gas hose still in the car or truck. Hose breaks and gas every were. The new pumps will shut off when their is a sudden increase in gas flow. But the two we have seen put out a couple gallons of gas before shut off. The hoses we have seen have a break away near the pump. Lots better than in the old days when the pump went with it. Getting the side of the rig sprayed with gas would be a nightmare.
Some states like Oregon you may not touch the pump. They fuel you and will not in most cases if you have not shut the fridge, water heater ect off.
We always shut down not because of any laws so much as for our own protection. Never know when a car will drive off with the hose still in it. Murphys law always rules..