That aspect of JK Rowling and her aspect of writing is what makes me love her so much.
I've read in an interview that she has more information about her characters than the entire series' mass combined. She knows that there is more to a story than just what happens to the characters in that one section of their lives.
I cannot wait for the Potterpedia to come out, it's going to have so much information about the characters.
And, I cannot wait to read what her mind creates next.