Since this thread originated as an attempt to present fact and dispel myth about the anamorphic process, I would like to help clear some misconceptions that have been presented here as fact.

nothing is squeezed into a frame in a DVD transfer. It's quite the opposite, since more vertical lines of visual information are added

This is utterly false. At no point in the entire DVD production process is any resolution added. This statement also includes the tape mastering process, where the master tapes (D5 and DigiBeta quite often, not quite as much D1 as there used to be) are telecine'd from film or downconverted from HD masters. Some, but not all, possible workflows for making an anamorphic master for the final MPEG-2 encoding:

Film --> Anamorphic SD Master
Film --> HD Master (may or may not be anamorphic; depends on OAR) --> Anamorphic SD master
Film --> High-res digital files --> SD tape master or SD files

There are myriad other variations, but the work pipeline is the same in that it is an ever-reducing process, and each arrow above represents a reduction in horizontal and/or vertical resolution. The bottom line is that nothing is ever added. When squeezing film down to 720 x 480, stuff is always subtracted.

Just wanted to help clarify a bit.