User blog comment:Care Level/Once again, on Attacks v. Spells./@comment-5035765-20150809203933

making AP champions' AAs scale off their AP makes it so that auto attacking is always the best course of action

hell, it'd probably make Nashor's Tooth the most OP thing in the game for AP champs.

and as Willbach pointed out, AP and AD are not made equally and have different strengths and weaknesses (AP is easier to get TONS of, but is hard to sustain off of and has lower ratios, while AD is a bit harder to get a ton of, but has a lot of really strong sustain off of it and always has at least one 100% ratio in auto attacks)