That's just it: they're not. Either the pump is out of calibration and the station is milking its clients or its being overfilled and they're damaging their EVAP system. I can't imagine the volume of the filler neck to be more than a gallon, so absolute best case you might be able to get 26 into a truck that wasn't run to failure. Seems like we're over complicating an otherwise easy system: fuel til it clicks and be done. If its more than 25 you have a dishonest station. I'd wager 99% of people either don't know their capacity or don't run it that low to notice. Try taking it to a national chain like Costco who is more likely to remove the pump calibration risk and see if you consistently get the same fuel amount.