Amazon are missing a trick here. There isn’t yet a good way to read graphic novels (comic books, you could say) in a digital way. Sure, you can buy graphic novels on the Kindle, but they are few and far between and certainly aren’t the popular ones. There’s no Walking Dead or Watchmen or even the old DC/Marvel comics.
But if they created a proprietary format (like they did for normal Kindle books) which could display comics well on an iPad or any other screen by automatically adjusting to fit the screen size, they could totally own the space.
Of course, there is the fact that most comic book artists like to lay out their books very precisely, with boxes overflowing others and such, but, still, I’m sure Amazon could do something good.