No, but many, many YouTube videos that are songs (either music videos or slideshow + song) have been re-uploaded and/or re-encoded many times, so often they don

No, but many, many YouTube videos that are songs (either music videos or slideshow + song) have been re-uploaded and/or re-encoded many times, so often they don't have a high quality option, or if they do you're watching a 360p re-encoded in 720p. If you've ever listened to a song on YouTube that sounded like it was being played underwater, that's what happened to it!