This is patently untrue. [etc]
I would beg to differ. Obviously if you compare all DVDs to all books, you'll find a quality difference. With the cost difference in production, and the ability to get published on either media being vastly different, there will be a difference in overall quality (with books coming out on top; that's just inherent in the production process). Although, this is much different now, with PDF manuscripts being released by just about anybody--and the quality has indeed dropped significantly now that anyone and their dog can release something through that method.
However, I was referring specifically to at least decent offerings from each of the two media.
I was thinking specifically about Daniel Garcia and his rubber band effects. He has a rubber band effect in print in one of his lecture notes, which I adore, but the issue I had with it is that it took a significant amount of time to understand all of the moves correctly. The rubber band effect that he has on video (his last release with E), however, was a lot easier to understand, because one could just follow along and see him performing each and every step in its entirety (rather than stop-motion pictures, along with a sometimes-confusing explanation; granted, DG was a lot more clear than some others who have effects in print, and it could have been a dreadful experience were it one of those other people).
The difference is the ability to see how each step is supposed to look in its entirety, as compared to the limited pictures and sometimes confusing explanations (even the good explanations sometimes take a few reads to understand; I've never had to re-watch a video explanation, however).
All I am saying is that video offers a potentially easier to understand media. Is it better? Not necessarily. But, depending on the person doing the explanation (and that is a big factor), video offers a superior media as far as clarity goes.
As a caveat, though, it also tends to be prone to people sharing everything that comes to their mind, as you mentioned. However, I would say that is an issue with the person doing the presenting, not the media itself. If they properly script their explanation, that shouldn't be an issue (this is usually why books tend to be so good, because people are forced to think everything through--there is no opportunity for "freestyling" a (good) book).
Either way, both media have their good and bad points. DVDs tend to attract a lot more people who don't think their stuff through very well, although PDFs seem to be catching up in that regard.
With that said, I prefer books purely because there are a lot of great gems that get overlooked in books. That's a point I (unlike most, it seems) actually like--I love being the only one performing certain effects. I say, let the current generation flock to their DVDs, it leaves more goodies for myself.