^They may or may not. Bear in mind, Ayu's PVs aren't really the simpiliest or lowest budget ones out there.
And TBH while a director should have knowledge of cinematography, a director isn't always gonna know the deep down specifics, like the director may know what kind of look he wants but won't necissarily know how exactly to achieve it. The cinematographer knows what film stock, lights/gels/lens/filters/materials, etc. needed to achieve the specific look. Again, a director could know this but not always.
I think some people are confusing what a director and cinematographer is. Like they have two complete different jobs, whether they are the same person or not.
Although isn't Ayu ultimatetly the director of her Pvs?
http://en.wikipedia.org/wiki/Cinematographer
http://en.wikipedia.org/wiki/Film_director