The Blu-rays of Alien and Aliens contain a 4.1 Dolby Surround track on them, are these reproductions of the 70mm 6-track mixes of those films?
Incidentally, the scene in Aliens where Bishop is ripped in half on the floor and Lance Henriksen's body can been seen was altered for the blu-ray release as discussed here:
This is an alteration many people seemed to accept but most people are against redoing the optical effects in Star Wars. Removing scratches and dirt is fine because these are imperfections that have appeared since the film was released and are not what was originally intended to be seen by the viewing public.
Any imperfections to the film that happened during post-production was originally deemed acceptable by the film maker and released to the viewing public. These versions might not be "acceptable" by today's modern standards but they need to be preserved for their historic value.