With all the free porn available, I'm curious as to why you would pay for it unless it's for a live interaction. Anyway, porn seems like a great industry to adopt bitcoin just for anonymity.
It might sound strange, but there are people that actually pay for porn because it's the right thing to do. This is especially true for smaller sites where the performer forms some sort of "bond" with the subscriber. In this case, the subscriber knows the performer makes a living selling her(his) movies online, and buys a subscription to support them.
A second porn payer, is the one who does not know how to find free porn (these people still exist, altough they are becoming less and less frequent)
A thirth kind of porn payer is the one who buys something that is hard to find for free (live porn, 3d, interactive, specific niche,...)
Well it depends on the site itself and the revenue model. Free sites still have click revenue or ad revenue.''
The third one makes perfect sense as there's a different experience...and I guess some of the older folks may not know their way around the internet...