I agree with Rob. Storaro said many times that there is only one Director on the set, so why would there be a "director" of photography? Why not a "director of sound" as well? I think the term DP ( or Director of Photography ) is much widespread, but Cinematographer is the one that really encompasses all the things that he/she as a professional artist does on a film. I don't think it has anything to do with the film itself, be it a feature, a short, a doc, or a music video. The job is the same.