@Kitabi,
You know what? I give up with you
You are trying to impose or think that the alternatives Kindle users have for buying their books is a Niche, that is 100% your opinion, that is what you feel and not the opinion of other Kindle users.
You were questioning and said, we can't read from other stores, that's simply untrue. We can, I can, all Kindle users can read and download from other stores without breaking any DRM protection.
You want to make people think that if your book is not ePub format you are stuck. The main issue here is about the DRM protection. Even if I was a B&N user and buy a book from Amazon, without DRM I could convert to ePub. So your argument is basically based on the preference and likeness for ePub format, B&N store and public libraries. That is what you like. There are other folks like me, who don't need anything from those stores. I actually sold my Nook because I was not able to download or get computer content from any place but Amazon; O' Reilly is the other good place and they sell their books in MOBI format. I have tons of books on my Kindle DXG from O'Reilly.