Originally Posted by Billi
With Amazon it's clear, they just took what Mobipocket had developed, but the question was why all epub publishers rely on Adobe.
They don't. B&N use their own DRM system which is independent of Adobe. And, as I mentioned in my previous post, Apple's ebook store also uses their own form of DRM.
One of the weaknesses of ePub as a standard is that fact that the DRM mechanism is not specified as a part of the standard. You can add whatever DRM mechanism you wish, and still call it ePub. So, from that perspective, it's a good thing that most ePub bookstores have standardised on Adobe DRM.