User blog comment:JmLyan/Tero, the Eagle-Eye/@comment-22636720-20140114052950/@comment-5860569-20140114125903

They do have AP-scaling on hit damage. However, both of the abilities you mentioned also have a side effect that isn't scaling on-hit damage: When you activate it, Miss Fortune gains bonus attack speed and grievous wounds on her attacks, and Varus has Blight, which is a key mechanic for his damage potential.