While it's a smaller market (and yes, it is. Way. A number 1 bestseller is barely worth a neilson point) it's already pretty fragmented. It's good that they're trying and perhaps with some luck they can get somewhere, but we're already talking post-itune/zune/et al universe compared to music. Nothing works well with anything else, except of course, if you don't pay for it and just pirate or stick to only the material specifically for your device. As usual, legal works need to be at least as good as their pirated counterparts to those who buy them, as in "if both of these were free and legal, I'd have no preference".