In my opinion, generally speaking, women use sex to get affection, and men use affection to get sex.... Ding, Ding, Ding....We have a winner. You should write a book (or at least a paragraph). All the physchobabble in the world could not have boiled it down to a more common denominator like you have. Questions is: Did you come by this from purely theoretical observation, or should I ask for details (LOL)
Actually, I wrote a book on how to attract the opposite sex - gave lectures and taught a course in college - It was a lot of fun, and I had many interesting experiences doing research and teaching ;-)