One of the reasons I chose the Barnes & Noble Nook over the Amazon Kindle is that the B&N Nook e-store sells books in the ePub format, which can be read on a wide variety of other devices and using other non-Nook software. I download the files of the books I purchase onto my PC or other storage device, and change the file name to the books title and author, without changing the format. (Although I'm way behind on this project at the moment.) So theoretically, even if B&N goes out of business, or even just shuts down their Nook support, I could still open those ePub files using any number of other software packages without relying on their servers.
On the other hand, as much as I use Amazon's services, I was never going to get stuck with useless piles of data if they stop supporting their proprietary e-reader software (KPF); never going to have a book disappear from my device because a license somewhere expired. It's the same reason I buy very little (music, books, video) from iTunes. I don't want to be locked into their ecosystem, subject to Apple's whims. I don't trust these large corporations to make decisions to my benefit. And that includes B&N; that's why I'm hedging my bets the best I can.