Putting the fuel into litres rather than percentage does bring a small issue with accuracy - if a car has a large fuel tank, you can be pretty accurate with how much fuel you're putting in, but with a smaller tank you're losing quite a bit of accuracy. Those who concern themselves with saving as much weight as possible might not like the idea of losing that bit of precision.
Using decimal places could work, I guess, but then you might have a bit of an issue using a fairly small slider to get a round number if you want one. Halves seem to be a good idea, with the slider going from 25.0 to 25.5, then 26.0 et cetera. I'm just thinking out loud here.
The most likely reason the fuel is set by percentage is that a percentage can be carried over between cars, and still be about right for the same distance - there are, of course, exceptions, but generally less economical cars have bigger tanks, and so a percentage set in a car with a smaller tank won't be too far out. A
very general rule, yeah, but it still exists.
Then there's the thought of what you do when there's, say, 80 litres in the tank of an FO8 and you select an FBM. The FO8 was nowhere near full, but the FBM would be way over the maximum, so what the hell does the gauge set to? If anything, it would use the percentage to decide. Isn't that where we started?
Sam