"And still no one’s perfected the trick of making a simple mobile device, smaller than a laptop, that will let you write, read and edit on the move."

I'm thinking you tagged it with your made to "consume not create" idea.  The controlling drive for these things seems to be tipped toward the passive entertainment end of the scale and away from anything that requires much void filling on the part of the user.

I'm guessing, the simplicity of what you are looking for will happen accidently in a quest for something else.