I believe that is hard coded so that you don't auto start and then end up with a dead out of fuel vehicle in the driveway... as well as -
Running down low adds heat to the fuel pump and shortens its life expectancy! (being submerged in fuel is its coolant. - even test firing a dry pump will ruin it in less than 5 seconds!)
J Wm Bishop EA, ASADE
The wagon should, of course, be as light as possible, but strength should not be sacrificed to lightness, for on any but the regularly traveled roads, the wagon will get many a hard knock...