Iirc they initially claimed 40 miles, because they were throwing that around for commuters who mostly drove less than 20 miles to work.
Sometimes you get stuck in stop and go traffic - accelerating, brake lights, AC/Heat and electronics eat power. Sometimes you circle blocks endlessly looking for parking. Then there are unexpected detours and errands. With my gas-powered cars, I've taken filled spare gas cans with me on really long trips, saved my hide a few times. But to worry about going 20 miles in one direction is nuts.