Serving content over the web assumes that the content will be downloaded by a browser for rendering. Control over what and how that content gets rendered is controlled by the user. I think this aspect made, and still does make in the present tense, the web what it is. That's why the browser is called a user-agent--an agent that acts on behalf of the user.
YouTube could also move to another protocol, or develop a proprietary one to protect its interests. Otherwise it feels like they want to have their cake and eat it too.