Hob:
I have a different understanding of the term anamorphic.
I thought it described a process to use all (or most) of the 480i scan lines to store or transmit an image that started as widescreen (2.35:1 or 1.78:1 or 16:9 or whatever) and is ultimately displayed as widescreen. During storage or transmission, if the "raw" signal was viewed on a standard 4:3 monitor, the image would appear vertically stretched. The DVD player or video monitor modifies the anamorphic signal to recreate the original aspect ratio and correct geometry for the viewer.
The whole idea is to take advantage of bandwidth that was otherwise wasted on a non-anamorphic letterbox program, which stores/transmits the horizontal black bars as if they had useful video content.
The end result of "anamorphic," a.k.a., "enhanced for widescreen," is more scan lines used for real picture information, thus improving vertical resolution when compared to non-anamorphic letterbox.
For viewing on either a 4:3 monitor with vertical compression ("squeeze") or a 16:9 monitor, all of the scan lines provided are used in the display. The DVD player should have the aspect ratio set for 16:9.
Side Note: There are some analog 4:3 TVs today that provide vertical compression to take advantage of anamorphic program material (Sony and JVC have models that I have seen).
For viewing on a 4:3 TV or monitor that does NOT provide vertical compression, the DVD player aspect ratio should be set to 4:3. For an anamorphic DVD, the DVD player creates a non-anamorphic letterbox output to display the correct aspect ratio on the 4:3 TV. In the process, the DVD player actually reduces the vertical resolution of the picture area and provides the horizontal black bars as part of the video output, just as if the source material was created and transmitted without the benefit of anamorphic processing.
So, a non-anamorphic DVD that has a letterboxed widescreen movie looks like 4:3 content to the DVD player and the TV. This would result in a widescreen picture surrounded by both vertical and horizontal black bars if viewed on a 16:9 monitor. If either the DVD player or the monitor has the capability of zooming the picture (stretching equally in the vertical and horizontal directions) then a viewer can fill (or nearly fill) the screen while preserving the original aspect ratio of the movie, recognizing that zooming a letterbox picture provides less vertical detail than the anamorphic alternative.
In short, anamorphic describes the process of using all scan lines to transmit or store 16:9 content with the expectation that the viewing equipment (DVD player or TV/monitor) will recreate the original 16:9 aspect ratio. On a 16:9 monitor this is accomplished by horizontal stretch. On a 4:3 monitor this is accomplished by vertical compression.
So, AFAIK, everything anamorphic is widescreen. But not all widescreen is anamorphic.