Easy. Porn stars have to be attractive to the people watching the porn. Different people like different looks, so a large variety of films are made with differnt themes. Also people are turned on by different things. In porn, the woman are alwys payed more than the men, thus making it one of the only official industries where woman make more than men. Ron Jeremy is famous for being a porn star, even though he is big, fat, ugly and hairy. There can't be that many people in the world who find that attractive, therefore the world is flat.