So Africa Twin and 1250 GS both get 577 km on a tank. Nice, very respectful for 100+ horsepower, 500+ pound beasts. And KTM with few bikes on the list. But, well, actually.

Honda CB125F has 11 liter tank and sips only 1.5 per 100 km. That gives it 665 km range. And it only takes half the amount of fuel to fill the tank, so you get 1330 km for the same money. You and 7 of your friends, if consider the purchase price of the bike.
This is nice to know even if these numbers are theoretical. At a higher speed, in a great headwind, uphill all the way, the distance is halved. Going slow, with tailwind and downhill you can go twice as far.
Reminds me of something a friend said long time ago, after having been almost 500 km from home with a large tear in the rear tire, having to be at work early next morning, the tear being held together with the last of the glue and slowly leaking. "When you really baby the throttle, the mileage on a CBR 1000 RR is incredible."
But the thing is that no one rides their bike until it runs out of fuel, and then starts to look for fuel station. Most modern bikes have fuel gauges and low fuel lights. These come on when 1/4 to 1/3 is left in the tank. I consider that the practical range. My CRF Rally, with a 12 liter tank, only takes 8 liters if I fill it up right after the fuel light comes on. Since it uses over 3 liters per 100 km I consider the practical range only 250 km instead of almost 400 km. Unless I fill the Camel tank too.