I know not everyone bought the trilogy on DVD. But did anyone else listen to the audio commentaries. Lucas mentions I believe in the commentary of Empire that it will be explained the difference between Qui-Gon and Obi-Wan. It has something to with their willingness to become one with the force. Since Qui-Gon was kind of liberal when it came to the Jedi code maybe he really was not willing to become one with the force just yet. I don't know but the audio commentaries give some good clues on the situation.