The point here is that a lot of times information that *is* on a disc isn't shown on the screen - a little bit always gets cut off the edges on TV screens. TPM was probably framed wrong as that was a 35mm transfer. Example from BEN-HUR:
Actual 70mm scan from the film:
Fixed aspect ratio:
Fixed aspect ratio with the DVD image over the top:
See how much of the image is lost there? That's probably what happened with TPM.