This could possibly be an explanation for the behavior of promiscuous individuals.
No, it couldn't. It's easier, faster and less complicated to achieve orgasm through masturbation than it is with a partner. If orgasm was such a powerful and addictive force of nature for humans as for rats, there would be less, not more, actual copulation going on.
The fact of the matter is that, as in so many other cases, human behaviour is more complicated than the sum of its physiological and chemical parts.
People have sex for a myriad reasons that change from person to person and from encounter to encounter - they seek pleasure, certainly, but they also seek attention, affection, physical closeness, affirmation of their body image, tension release, ego gratification, revenge, oblivion, company and comfort - and these are just the ones I know from personal experience. I'm sure that there are at least as many reasons to want to have sex as there are people in the world.
It's true that orgasm is a clever trick played on animals to encourage them to reproduce - but there's no need to be so smug about it, because it is not the be all and end all of either sex or evolution. Take your eyes for example - they're a major evolutionary breakthrough, the benefits of sight are obvious - but they also play a crucial role in the choosing of sexual partners, and hence of course reproduction. A similar case can be made for all the senses, as well as more subtle agents of physical perception like pheromones.
Nor, on the other hand, does the orgasm's role in perpetuation of the species serve to detract one iota of the full power and beauty of the experience, especially when coupled with intimacy and affection. I get the annoying feeling that DMan is metaphorically trumpeting his findings on orgasm as a way of shattering what he thinks are other people's romantic preconceptions - but cynical people can have preconceptions too, and they're just as wrong. Only not as much fun.
In one of my recents forays into the world of evolution, I picked up an interesting fact: having an orgasm during intercourse increases the chances of fertilisation. Apparently the rise in body temperature is good for the sperm, and the vaginal convultions help it along and upwards. So orgasm isn't all about pleasure, after all.