On the surface the conditions even almost seem ideal - you have an existing oligopoly where each player has huge overheads and then on top of this add huge markups. You have a somewhat captive market (the students are entirely captive, while the professors are generally pretty free to choose the books that they want), and a product that's targeted towards younger, educated people (people to whom technology isn't a huge burden).
The only thing that's really standing in the way of someone shaking things up is in convincing the professors that your option is better than whatever's being offered by the incumbents. I really, really hope that at some point soon someone takes on the publishers - with a serious product, they'd have the potential to win, and more importantly, to do something useful for making education more accessible.