My 2010 MINI (BMW-made) has the same deal, and you could use the stats it gives you (kilometres until empty, average kilometres/litre, and actual tank size in litres) to calculate what's left in your tank, but why not just add it to the displays that already exist?
I also notice European cars (Audi, BMW, MINI, Saab, even VW etc.) tend to be more accurate and linear than American/Japanese vehicles. But that's just me.
When I was a kid my family had a Mercedes diesel and my aunt had a Cadillac. I remember noting that the Mercedes fuel gauge was labeled "Tank" and marked off in a round arc with equal distances between each of the markings. The Cadillac had a square gauge labeled "Fuel Data Centre" with a needle sweeping across markings in a straight line. The Mercedes was much more practical.
I also notice European cars (Audi, BMW, MINI, Saab, even VW etc.) tend to be more accurate and linear than American/Japanese vehicles. But that's just me.