This move has nothing to do with usability or device capabilities or software support. The only reason for turning them off is to remove a hole in their DRM. These old devices allowed you to remove the copy protection from their books (hardly anyone else uses DRM these days anymore). Removing the old devices makes freeing your books from DRM just much harder.
> hardly anyone else uses DRM these days anymore I thought that all the major ebook stores had DRM on most purchases, and it was just a few indie publishers choosing to be DRM-free. Has that changed?
In my experience soft DRM is very common, hard DRM not so much.