> They don't use HTTP. HTTP is used to bootstrap the player, not to feed the content. The content itself is served over another protocol such as RTMP and that protocol is a streaming protocol (it sends chunked data) and it wasn't intended for downloading files and writing them to disk as a singular binary blob. Obviously it can be used that way but it's fair to say services like youtube-dl are using the protocol in ways it wasn't originally intended to be used rather than content owners serving content on a protocol that was always designed for distributing files.
Not true at all, most YouTube videos are offered as plain webm files.
Also, keep in mind that recording TV's is legal.