Not a fill, but there is background for this in the EU. In that Luke names his son Ben after his first jedi mentor and Han and Leia's son who goes dark is named Jacen. Luke always knew Obi Wan as Ben, so it makes more sense for him to name his son Ben instead of Obi Wan. What the thought process was in switching it for the movie, I don't know, but I'm sure someone will ask JJ soon.