As far as the direct transmission thing goes, I've realised that in some styles of Qigong and Feng Shui, teachers may speak about a principle called Yi, which has to do with oral transmission of certain concepts and secrets that are mainly of a mental/psychological nature that can be applied in a physical form.
As far as they are concerned, videos and books do not contain this "Yi" as strongly as the "breath" or "Qi of the teacher". As such, these concepts are not conveyed except by word of mouth on a personal basis. Books and videos are hardly, if ever done on these concepts, and publications are almost never encouraged by some masters.
I have personally experienced this phenomena while training under two different Qigong teachers. It was really strange to tell you the truth. One was very adamant about not having any kind of published information, for fear of losing the quality and spirit inherent in the training.
The other was a bit more modern in thinking and utilises videos and books, but warns that any practitioner should be trained first by himself personally, or one of a few people he has trained to teach his style of Qigong.
Hope this applies to what we're talking about.
My 2 cents.