Widescreen Enhanced DVD vs. Standard DVD
Below are frame captures from the two Tron DVDs. Both were captured at 720 x 480, which is the native resolution for DVDs.
The first image is from the new 20th Anniversary DVD. The disc was mastered as a widescreen enhanced (anamorphic) DVD. This means that the video is mastered at a 16:9 ratio, to fit a widescreen monitor. Since Tron is 2.2:1 ratio, there are small black bars at the top and bottom to compensate.
The above image appears stretched, since it isn't resized to a 16:9 ratio. This is how it would look on a widescreen TV:
The next image is from the original Tron DVD. The video is mastered at a 4:3 ratio, to fit a standard monitor. To compensate for the difference in aspect ratios, the black bars at the top and bottom must be much larger, and the part of the picture devoted to the movie is much smaller.
The image appears squashed, since it isn't resized to a 4:3 ratio. This is how it would look on a standard TV:
For movies that are widescreen originally, anamorphic DVDs are the way to go. Even if you have a standard TV, the picture still tends to look better, since you're starting out with more detail in the first place.