I think these monolithic files are provided only for up to 720p quality, mainly for compatibility with older Flash players. To download the maximum quality with youtube-dl, you have to use "-f bestvideo+bestaudio" - then, youtube-dl will download both streams, and merge them for you with an ffmpeg invocation.

Ha, I never paid much attention to higher bitrates, and most of the time I only see resolution up to 720p (maybe because of my tastes).

I'm sure there are ways to merge streams on the fly though.

There has to be some way, the player on the YouTube website does it. :)

yes. you can force the streamable mpg4 download with the -f option (-f22), but it seems not all videos are encoded that way. livestreamer might be the tool of choice if you don't want to use your browser to watch a youtube video.