Turning off your engine while fueling is prudent and required. But as others have pointed out, the other vehicles are permitted to come and go while the pumps are operating. My ignition coil and spark plug wires are a good way away from my fuel inlet, it's the other vehicle behind mine that has these components close. Consider a car with the filler under the rear license plate, and the front engine vehicle who crowds him in order to get the hose to reach (they've gotten shorter lately). He'll probably rev the engine a couple times before shutting down for good measure. Ever fire up your engine in the dark and look under the hood? (a good overcast night is a good time to check your ignition system) An older vehicle can have quite a light show going on.