I think maybe part of this debate is because, as is often the case, we are talking past each other and not truly understanding each other.
1) I agree that different video recordings of audio systems sound different (how could they not?).
2) I agree that if only one thing in a system changes, and if everything else is held constant, then a before video and an after video may reveal a difference in sound due to that change.
3) I think the disagreement is about the meaning, and about the meaningfulness, of what these sounds on videos and differences in sound mean. I do not agree that one can understand the sound of an unfamiliar system — as if you were in the room listening to it play an analog recording on vinyl — by recording digitally on a cellphone a video of the audio of that system to a generic ADC in a cellphone and then playing back digitally the video through a generic DAC on a computer. I believe that far too much low-quality digitization has occurred for one to pretend that one is experiencing a sonically authentic and technically valid facsimile of the sound of analog playback on vinyl in person.
Ron, a phone video is a tool, nothing more. No one is claiming that such a video sounds the same as hearing the system live.
I agree with you that there is a disagreement about how meaningful such a video can be. I happen to think it can be very meaningful when understanding what one is hearing, the inherent limitations, and how to use that information to make judgements. One has to understand how to use tools and then to use them appropriately to his advantage. The video is limited in a sense, but it can also be very powerful.
It is like getting a protractor and other various cartridge set up tools. There are different levels of understanding how to best use these tools for optimal results. Same with a specific set up LP. It is important to choose the right one for the task. One has to know what to listen for and why, and then what adjustments to make. Sometimes this can take a long time with many trials and practice.
Add to all of that the fact that some people are simply better listeners than others. They might also have greater knowledge and experience enabling them to find more meaning from these videos and to help them understand what they are hearing about the specific system and room depicted on the video.
You are assuming that videos only have meaning when used for comparison purposes. I do not think that is the case. Sure comparisons changing one variable can be audible, but one can also learn from hearing the system video in isolation, or two videos of completely different systems and rooms. It just depends on if you are assessing a particular component or set up change, or assessing a whole system or room effect.
I discussed with two fellow members how two different power cords to my turntable motor sounded different via two videos. We then discussed one cord sounding different in two different outlets. I can listen to one video of Tang's new speakers in David's system and room and know that it is a great design. Baffle material changes were discussed via video. I can then listen to that video from David and compare it to some of Kedar's videos and form an impression of specific aspects of the different systems and how they compare.
The understanding can certainly be meaningful, as it was when I discussed my old speaker set up issues with David via video, or the recent power cords, but the videos are not comprehensive. Like most good tools, they do not tell the whole story, just a part of it.
Bonzo is right, this discussion will be the same in years to come.
By the way, what do you mean by "Acoustically -Coupled"? Simply the audio track in sync with the video track? Is this your complex way of describing a simple system video may by phone?