My SO and I both agree that a good mutual back scratching session is better than bad sex. I dimly remember a similar opinion behind reached in IMHO a while back (though it could have been on an entirely different forum, too. Beer drinking does that to your noggin’ :)).
The question is why ? Why does getting one’s back scratched feel so good, and why does scratching other body parts not trigger the same pleasing sensations ?
I don’t dislike a backrup but I’d rather have my back scratched then rubbed. I’m like a cat that way, I love to get my back scratched. If I win the lotto, then someone is gonna have a job as my personal back scratcher
I’m going to make the perhaps unwarranted assumption that you (the OP) are human. Assuming that to be true, I’d say the answer has to do with our primate past, when we’d all sit around the savanna and groom each other. Couple that with what Nunavut Boy says (pair bonding and intimacy and all that) and I’d say that’s going to be close to the answer.
Personally, my wife likes me to comb her hair, and a back rub is more a caress than a rub in the XT household, but I think it’s all part of the same thing…