I agree with the above statements. On a similar note, when watching Alec Guiness in ROTJ he looks so much older than ANH. Understandable since it was filmed many years later but man it looks like crap IMO.
As far as Liam Neeson, I remember an interview when he was asked if he would reappear in AOTC and he just smiled and winked during the interview, which in turn I thought was going to be a scene that was very secretive as to surprise the audience. Like said above there must of been a major head butting with Lucas on the fact. I thought for sure that he would appear, filling in a major gap and explanation that really still has not been touched upon.
Who knows, maybe during the TV series this will be explained. Although we know Qui-Gon taught Obi-Wan on Tatooine I could never see them appearing due to the money situation. But maybe some day when their careers are washed up it might happen when they need work. Especially since I dont see the TV show happening any time soon.