For math, I agree with Nate that screen shots are often more accessible and allow the student to spend more time looking at each step. Screencasting is another possibility in certain contexts… slideshare with audio commentary could be particularly useful.

And frankly, demonstration of a particular math process is probably done better as a series of stills than in a video. Unless there is something significant about the timing of the steps that the video is required to demonstrate, or some peculiar movement that is better seen than described, the video you mention — while probably useful — contributes nothing more to the process than a series of a dozen still screenshots might. And the screen shots wouldn’t have required you to use a player, nor would it have created the kinds of frustration you felt from not being able to see the video in the beginning.

I’m sorry, but I think your example demonstrates my case for “no value added” than it does yours for “it could be helpful.”

Remember, the point of media selection in any situation is to pick the most effective technology and that usually means the least complex. When given a choice, always pick the simplest technology that meets the need.