Why do so few Rh negative relationships exist?

While on Datebytype.com connections are easily made, it seems that in the offline world few Rh negative relationships get formed. Of course, being the minority, a larger selection of Rh positives exists, but what if there are other reasons as well? What are you looking for and what do you THINK you are looking for in relationships? What have you learned to be insignificant that you once held high on the list? What advice would you give to young Rh negatives yet to have their first real relationship?