If they do depend on the sales of BoS videos, I'll not complain, Although, BoS is one of the best conferences I won't be able to go, and I would love to watch the keynotes for free.
In most cases they are though we may get asked to not release a video to the public if a speaker has said something that they wish they hadn't, in one case a speaker discussed a company that they then started teaching an MBA class on and realized that the students could just watch the video instead of doing the classes, someone was once very unintentionally indiscreet about a co-founder and some investors...
We try to respect the wishes of the speakers.