The only way I can rationalise these sorts of comments - maybe these people have had an experience that they need to work through (a difficult birth (hence the birth horror stories), a hard time breastfeeding (hence the rough up your nipples etc comments).
You'd think they'd talk to people close to them - but maybe there is no one. Or maybe they've spoken to people, but still have more to get out. Or maybe no one has listened.
Maybe, just maybe, with some of these people, if you listen for a short time they'll go away! Its in the same category, for me, as the people who touch and rub your belly when you're pregnant. So out of order!