Ancestry.com and several other related entities are basically outreaches of the Mormons. Part of their theology includes baptizing of the ancestors of members of the Church of Jesus Christ of Latter Day Saints. (i.e., when you become a member, they will baptize as many of your ancestors as you can name to make sure all end up in heaven together or something.)

They provide a service to you and charge you for it, but as you build your family tree, that's information they will charge other people for and not pay you a dime for your work. I found a relative that has done extensive genealogy investigations and provided me with information about my direct ancestors. He asked that I not provide that information to Ancestry.com or any other site because then they will turn around and charge others for his work. You may feel it's a fair exchange; my cousin didn't.