I'm assuming you are talking about YouPorn. I'm surprised they went from Perl to PHP. But they obviously know what they are doing. I wonder if they use HipHop at all.
Like stated before, most adult website owners are average joes, and PHP being easy to learn with a low entry barrier it was the logical reason to get a site up and running fast. Also because many of the tools written for the adult industry were done in PHP. Just like ICQ it won't ever be replaced as the standard for the industry.
From what I recall its essentially how people do business. Everything from technical support with adult oriented hosting companies to making deals to sell sites/traffic/etc or talking to sponsors about promotions/etc. Plus a great deal of just general bs-ing. You have to remember outside of maybe a dozen large companies, most adult sites are just run by 1 or 2 guys so its their form of talking at the water cooler.