PDFs and comics are not a small use case at all - the push to larger screens is mostly driven by people who want to read scientific papers, business documents, etc which come in pdf form, or manga and other graphical works (the drive for color ereaders seems to come almost entirely from this segment). The smaller "ebook only" readers are much cheaper and marketed less aggressively.

> Graphics and PDFs are much lower on the priority scale.

Unless of course you read books that have graphics or come in pdf form.