Personally I prefer the third one, I think it stands out more than the first two, and the last one seemed too 'shiny'.
358 karma · joined December 5, 2012
Lipson-Shiu: ICUE
It covers more then just recommendation systems - but has some real gems.
Since it is mainly producers and official videos that do not show up, my first guess would be maybe allowing playback on mobiles used to reduce Ad-revenue. I remember a while back certain devices could not display ads during videos.