You are quite correct, apo lenses are fully corrected only at the design distances. But being fully corrected (three-color correct) at any distance means they have a better chance at being better corrected at macro distances than lenses that are corrected for two colors at design distances. I'm sure there are paritally- or uncorrected lenses that perform wonderfully at macro distances, but in general, apo lenses do a little better. This observation may be due to the fact that there are a lot more apo-corrected long lenses than short ones, and long lenses always do better at macro distances. I have never experimented with wide-angle macro work enough to test the apo vs. non-apo lens differences.