Web & Application Design: we've been designing for a very specific use case
1. seated close 2. relatively large screen 3. precise mouse
If you take any of these things away... you can no longer cram functionality into screen space as we currently do.
It is the reason behind responsive design and the "mobile first" approach. You take away the precision mouse and the large screen and you have trouble. I'd actually say true screen size isn't even as much of an issue as is the precision (or lack of) of your finger. Especially considering you can put the mobile phone very close to your face.
In principle, mobile design is even similar to the other end of the spectrum, TV design. Although the screen is large, you sit far away, effectively reducing functional screen size. Throw in the use of a controller or even gesture control (i.e. Kinect) into the mix and the similarity between mobile and TV is even more striking.
It seems we've been designing for a very specific use case that is currently changing with phones, tablets, and even smart TVs. But do you think the "sit close, large screen, precise mouse" design paradigm going to fade away entirely? I suppose perhaps it can't because of productivity applications... but I wonder if there will be an upheaval there? Will see cluttered screens and toolbars give way to cleaner interfaces (everywhere)?
And would that even be beneficial? Or akin to trying to fit a square peg into a round hole?