With Google, Apple, Amazon and others all selling ebooks, you need different software for each one. This is because each seller has their own DRM to lock you in, and you either need a different device for each store or a general-purpose device with apps for each store. And you'll notice that each vendor does provide free apps for desktops and phone operating systems, too. That tells you the devices and software are not the major revenue stream; it's the books themselves. So each camp wants to get you hooked on their format and locked in so you only buy books from them, and book sales is where Amazon rules the roost.
Cross-compatibility would help any one camp win the format war. It is in Amazon's best interests to break or even support ePub DRM, making the Kindle compatible with Google Books and the Apple iBookstore, but the Digital Millenium Copyright Act means they're not even allowed to try. However, if someone were to publicly demonstrate that the ePub format is cracked, publishers might be less willing to support ebook sellers other than Amazon.
Now, for publishers, before any one format emerges as the winner, it is worth their while to support them all, and that's pretty easy, so they'll keep doing so. That means there's no differentiation between the ebook stores. Since there's no incentive for publishers to support one store over another, you can bet each store will be negotiating for exclusivity deals with publishers. That's when the wheels start to fall off for consumers. If some books are only available from certain locked-up ebook stores, but you want them all, you'll end up having to work with both, in much the same way as dedicated gamers own an XBox, a PlayStation and a Wii.
I really hope we can sort out this format war sooner rather than later, and I hope in the meantime I don't spend too much money on the losers. I don't want to get locked to a format that will die in a year or two, with a ton of ebooks I can no longer read. In the end, I support Amazon, because even if they fail, they can just switch to the winning open format, ePub. Any books I bought before their victory should be converted and still available afterwards on the same platform.
Mokalus of Borg
PS - I really don't like that situation.
PPS - But what can you do besides not buying any ebooks?