Cindy, I understand rescues (or any organization) must have some type of policy. You indicate that yours was based on statistics. Her's a link to an article (with statistics) about centenarians.
USATODAY.com - Centenarians increase in age and numbers
Nancy, great post. There have been studies that show that owning an animal may contribute both to the the quality and length of life. We don't come with an expiration date and I would feel empty without a dog in my life and hope to have one (at least) all my days that I can give the care they need.
I do think this whole thing is a new area to consider from a breeder's point of view. Of course, any responsible breeder would never refuse any of their dogs a forever home, if need be. Things can and do happen to us at any age.