I don't know if that will help, but I once had a girlfriend who had plastic surgery that reduced her breasts' size. One of the side effects of the surgery was the loss of nipples sensitivity.

And remember: these things can be extremely personal and individual. I don't see anything exceptionally wierd in a woman who doesn'y like her nipples touched. I guess it's not so different from women who don't like their ears or necks touched, as opposed to women who takes great pleasure in thouchs like that.