I think the point is the relative proportion of available/consumed porn that falls into these categories. Anecdotally, I agree with CodeMage that this sort of porn seems to be the predominant form (at least within the commercial variety of porn advertised on the internet). Perhaps what's needed is some sort of measurement of the different classifications. I really think you should address the point of proportion of this type of porn consumed, rather than the methods that can be used to identify it.