Oddly enough, porn is/was no longer the predominate traffic on the 'net. P2P traffic is.
There are lies, dammed lies, and stats, and depending on how one expresses a given protocol as a % of "what", (ie total bytes or total transaction transfers), one can argue between P2P and email, notably spam.
However, it is worth noting that the largest customer segment (ex telco's) of a certain well known infrastructure manufacturer was "anonymous", and widely suspect to be the adult entertainment industry :-)