I am in absolute agreement with the necessity for feedback. When I say it is possible to learn body mechanics from a video, I mean working with a training partner to emulate the video and test what is working and what isn't. You definitely can't just watch the video and have the skills magically implant themselves.
In fact, I'd go further and say that working with a (sometimes non-compliant) partner is essential for learning no matter what your source for the material is. Even if you have a teacher. You may have a great instructor, but if all he does is give you corrections while you punch the air then you will never gain the understanding that comes from working with a live body.
This is precisely our approach at Hapkido Online and thus far it has been effective for many people. Non compliant uke, quality video instruction, and close monitoring from an instructor. It works.