In a recent article, Wired Magazine's Tim Carmody ponders the reason that eBooks, and other electronic gadgets, are the size that they are. His conclusion: Sheep.
Carmody directs readers to the blog Got Medieval and blogger Carl Pyrdum for the explantion. Today's book sizes are determined by medieval book makers who used sheepskin, calfskin, or occasionally, parchment. The size of the medieval page corresponds to our modern books and devices.