All those distances that have a competitive time that brings you into needing the aerobic processes (>30 sec) do need that their aerobic capacity is developed. So a 400m runner needs the aerobic capacity too. Now Marathon is special in that it is way above 1 hour race and will depend a lot on fat metabolism so it relies heavily on the easy run and highly developed aerobic capacity. A 400m runner depend a lot on the anaerobic processes so the emphasize is different and less on aerobic training, but it is still a key part.
800m depend substantially on anaerobic processes, but at least 60-70% of the distance one relies on a well developed aerobic capacity to work with lactate. So it is the major part of the capacity even if the speed and anaerobic work is very important for the 800m runner. For the 1500m runner, it is the aerobic capacity that is the main thing, even if he/she needs to be fast, have a well developed anaerobic capacity and so on.
So I guess below 400 it is of less importance, but above it is the most important