I think it's a style exaggeration born form animation.  Similar to how innocense in anime is often reflected in eyesize even though no one reacts to the differing sizes within the same production.

I also think there is predisent in american comics by artists like Bart Sears (if I am remebering his name right) over vascularity for dynamic Bodies.  Sort of like how all comic females have tiny waists and huge.. you get the point.