gas pump settings

My wife and I just returned to southern Virginia after spending ten ice cold December days in Michigan. We obviously had to fuel up several times along the way. Because of the cold I became acutely aware of what would be considered a minor problem in Virginia, and that is this: Most gas stations want you to prepay when paying with cash, and I understand why, but why do they set the pump slow down settings so far below what you have paid for. For example; Say I purchase thirty dollars worth of gas. The attendent sets the pump to stop at thirty dollars, but the pump starts slowing down around twenty nine dollars and sixty five cents. I stand there freezing my balls off while the pump slowly clicks away the remaining thirty five cents worth of gas. Surely they can set the slow down settings somewhere near the stopping price, say twenty nine ninety! Are they hoping that the customer will get pissed and just stop pumping therefore giving the station owner a few extra cents? Or do they get their jollies looking out of the window watching the customers pull their heads down inside their jackets like a bunch of turtles pulling their heads into their shells, while the pump very slowly moves toward the stopping point? "Lookit that dumb sumbitch Earl! He's a freezin' his gonads! Them Virginny boys is dummer n a box o rocks! hee hee!"Several times during our trip, I stood watching the pump slowly move forward and thought to myself that pumping the remaining gas all over the pump and lighting it on fire would certainly help keep the rest of the frozen customers warm!! hee hee!