I think Lurtz's post is spot on - yes, paid sex is in some ways an abnormal activity, but it's something that you can get used to & can be a lot of fun. I certainly was no great shakes sexually when I started, quite often came too quickly and found that nerves spoiled it for me. With not much in the way of build-up, the orgasms I had were pretty inferior to what I could achieve when wanking. However, I got to know one WG & saw her often, I became more relaxed about the whole business and started to enjoy it more. Yes, sometimes I did decide to save my money, stay at home & have a wank, but masturbation can be unsatisfying, I prefer the involvement of a sex partner who's up for some fun! I can enjoy the feelings build up when masturbating, but it's a lot more exciting through sex.
Another job point made was that sex can be boring or routine - I had several WGs who have seemed uninterested, and just been going through the motions. However, I have also met plenty who have been very friendly, made the whole experience fun and sometimes really enjoyed themselves into the bargain. That's when it can be really special.