Fundamentally human vision is landscape. We live in a landscape. Interesting things are generally to the left and right of us, not above and below.

I think one day phone cameras will have square or cross-shaped sensors and you'll be able to easily shoot landscape video while holding your phone vertically.

For viewing, I think it isn't the physical rotation of the phone that is a pain - it's selecting the full-screen option, or the rotate controls. The latest Android makes this better, but I hope in future apps will just play landscape videos in landscape irrespective of the phone rotation.