In Hindu and Buddhist traditions, which is what a lot of The Force and Jedi religion is based from, when a person "leaves home" to become a monk he takes a new name and is no longer his old self.  He no longer identifies with his past or associates with anyone from it.  Vader was no longer Anakin--or at least that's the way it was supposed to be. 

http://www.adherents.com/people/pl/George_Lucas.html