A super-sharp, super-portable screen would be used to read all day long, but most of us won't spend most of our time reading anything recognizable as a book on them.
Take the record album. Everything about it is technologically pre-determined. The technology of the LP demanded artwork to differentiate one package from the next. The length was set by the groove density of the pressing plants and playback apparatus. The dynamic range likewise. These factors gave us the idea of the 40-to-60-minute package, split into two acts, with accompanying artwork. Musicians were encouraged to create works that would be enjoyed as a unitary whole for a protracted period — think of Dark Side of the Moon, or Sgt. Pepper's.
No one thinks about albums today. Music is now divisible to the single, as represented by an individual MP3, and then subdivisible into snippets like ringtones and samples. When recording artists demand that their works be considered as a whole — like when Radiohead insisted that the iTunes Music Store sell their whole album as a single, indivisible file that you would have to listen to all the way through — they sound like cranky throwbacks.
The problem, then, isn't that screens aren't sharp enough to read novels off of. The problem is that novels aren't screeny enough to warrant protracted, regular reading on screens.
I'd try to rebut Cory, because I do think he's wrong, but I wrote this post halfway through reading his article and edited it while watching a movie.