Sidney Furie and Otto Heller beg to differ:
THE IPCRESS FILE - 100 Cinematic Shots from Vashi Nedomansky on Vimeo.
Landscape may well be the most convenient format for a wide variety of shots, but it is in no way The Law. And it is a low blow to claim that because these YouTube contributors are amateurs they must therefore be Doing It Wrong. They are making a creative decision every bit as valid as any photographer would. The fact that it’s a moving image instead of a static one is almost entirely irrelevent for most of these shots.
(Shoot. How do I get Vimeo vids to embed properly?)
Edit to add:
Thanks, OtherMichael!