Only one use case I can see ( other than phone) for portrait, and that is to be able to look at my photos in landscape or portrait depending on how the photo was taken in the first place. A portrait photo on a wide screen device sucks.

Most people have a landscape use mode built into their brains from a early age cause they all use cameras in portrait mode, and its not a problem to hold. And hey they rotate their wrist to take portrait pics.

I think the argument about one handed use is crock. just watch i phone users in action, most go two handed in either orientation when it comes to selecting things, cause the thumb dont reach across the whole screen real estate one handed. Keyboard work needs two hands cause its faster even in portrait