Physical books are not files. Files belong to bureaucracy. Books belong to children (or the child within us). Books are about creativity, about counter-culture and overthrowing rotten ideals of our society. Files are about encoding those rotten ideals and forcing them on us.
So why should an e-book book be a file at all?
Food for thought: Do files masquerading as e-book pass the Occam's Razor? Is the reader of the future expected to understand words like file, format, device, disk, compatibility or OS?