Pain and D/s

R and I were discussing this last night on the way home from the MBBDSM Munch. Why is it that so many people in the lifestyle equate D/s with S/M?

I posted this question in the submissiveforum and I await the answers with great anticipation. In the mean time, I thought I might try to hash this out for myself.
I am not a masochist, at least not a very big one LOL. I like a good flogging, so long as it is more thud than sting. I like nipple clamps and biting and hair pulling, but none of those in extremes.
Because I am not a masochist, I find pleasure in other parts of a D/s relationship. I receive a tremenous amount of pleasure from pleasing my Sir. It is for that reason that I withstand more pain than I find pleasurable. I know he is a sadist and knew that from the start. But I also have found ways of pleasing him that do not involve pain and he is learning that he can like those things as well.
I find pleasure in touch. I love to touch and be touched--with and without implements. A soft hand run over my body can bring me closer to subspace than any spanking ever will.
I find pleasure in my submission. It is a great joy to me to turn myself over to my Sir upon entering his home. When I remove my clothing, I remove the stresses and problems that dog me during my day and I am simply his for the afternoon.
This isn't necessarily everything that I'm thinking on the subject, but for now, it is what I can collect into coherent thought.