How come this is not available as an e-book? Would look great on a tablet or color e-reader.
Probably because it's not a traditional e-book. Half of the appeal of the Book of Cain comes from all the drawing, backgrounds, and additional comments written in the margins. While I agree it'd be cool on a tablet, it would have to be something else than simply the text of the book (which would require more time for Blizzard).