The revised ending removes the important ambiguity.
This post contains MASSIVE SPOILERS!
I first saw this film when it aired on NBC in 1985. I was 8 at the time and found the whole thing very disturbing. The "revised" ending that was shown on that initial broadcast showed the terrorists tied to their seats, one rushing forward and being shot, followed by the female terrorist and the policeman being killed. Pretty heavy stuff for 1985, but who could blame the gunman? He was rushed by one terrorist, shot the other because she cried out, and then killed the police fella in the confusion. This kind of negates the whole conversation the passengers had just had about whether to execute the terrorists or turn them over to the authorities. The whole scene is very visceral and one can't help cheering as at least two of the terrorists still alive (one had been killed earlier) got what they deserved. Shame the passenger with the gun didn't kill the third piece of garbage.
However, the original ending (which was rejected by NBC but aired overseas and sometimes in subsequent US airings) maintains the moral ambiguity that is central to the story. We see the legs of the terrorists dangling...the passengers have executed them by hanging. This is slowly revealed as we see row after row of passengers sitting pensively in complete silence. It is chilling. We're left to ponder their actions, how they will justify them to themselves and to the authorities.
The original ending is less immediately satisfying (I admit, even as a child, I cheered as the passenger gunned down two of the baddies) but it is so much more powerful. Such a shame that ending is not included on the DVD-R release from Warners.