What happens when you get popular on YouTube? People try to jack your content.
I guess one of the things that comes out of this is the failure of YouTube to have any real lock on the content. They don’t really do any real “streaming” — the actual flash video files are downloadable (and thus you get things like TubeSock)
If you have a secure streaming player (content is streamed using a password protected protocol), it’s a harder infrastructure to build, but it prevents things like this from happening, and it makes content rights holders happier.