I addressed this earlier, BB. These are over simplified sources that don't know the biological details of the human reproductive system. In addition, the role of nipple stimulation on oxytocin has been known when it comes to milk let-down reflex, but more recently it's been found to play a bigger role in fertilization, assisting the sperm to reach the egg.
And, just to thoroughly muddy the waters of this discussion... Men are also born with milk ducts in the breast tissue. It's just that testosterone inhibits branching and further development of the milk-producing glands necessary for breast feeding whereas estrogen tends to increase such development. Just thought I'd throw that in there.
