Not everything is available digitally--mail, for instance. Sure, given the choice, I'd choose an existing digital book over one I scan myself, but I can't for instance choose a digital version of the medical bills the hospital mails me.

That said, this isn't an entirely unique concept, and you're right, positioning the camera is challenging. There are tools to help with this--arms and stands that position devices at the correct height to photograph a standard-sized sheet of paper. It may strike you as entirely impractical, but I remember the days when scanners were huge and bulky things, and even now when they aren't, I don't necessarily have the desk space to keep one out, or the desire to hook it up and store it when not in use. A reliable camera-based OCR solution for my Android phone and an arm/paper guide calibrated to the S III would rock, and assuming reasonable material prices and standard markup (I.e. not the absolutely huge markups of AT) it'd be competitive with dedicated OCR solutions and hardware.

Source: I'm blind.