HM
This answer should be longer, but the mixture still needs to be adjusted in fuel injected engines for the same reasons you need to adjust the mixture in a carbureted engine, to lean out the fuel supply as you climb. Just because it is fuel injected does not make the system any smarter, you simply have better atomization of the fuel, and therefore better or more complete combustion.
You are quite right about car engines, and until FADEC (Fully Automatic Digital Engine Control) was introduced, piston engine aero technology was stuck in the 1930’s, primarily because of short sighted regulations, and the controlling authorities unwillingness to change.
New piston engines that are FADEC equiped use one lever power controls, computers control fuel mixture, ignition advance, manifold pressure, even prop pitch. It also monitors and controls cylinder head temperatures, by adjusting manifold pressure and mixture.
IMHO, it was a long time coming.
Regards,
White Bear.