It's just that I'm predisposed to think of Casablanca (and Citizen Kane and the other movies ranked as among the best) as high art--and so a lens which looks at the movie(s?) as low art is sort of disorienting at first--Casablanca is a classic, Rocky Horror is a cult film. Which really works for your Shakespeare comparison, since his plays are also an example of texts which are in many ways low art but have somehow become immortalized and idolatrized as high art. Which isn't to imply that the high art/low art distinction isn't anything other than a sham, of course.