After following these developments for some time, I can not keep quiet any more...
My completely uninformed
oppinion is the following:
Every mobile book company would like to make the iPod of books. The iPod had 2 things going for it: a great user interface, and iTunes, which let people easily, legally, and cheaply, buy music for their iPod.
I bet that book publishers are at least as scared of mobile readers and digital books as music companies where/are of easy access to mp3. From all these stem the insistance of the readers on DRM, and why the advances in the technology is proceeding at snail-pace.
I bet that behind the scenes, there are fierce negotiations with publishers going on, which the book reader companies see as essencial for their success.
My feeling is that buggy software, and buggy websites (sadly) have not yet prevented a launch of a product. And, it is easy to say something like "we are working to make sure that the software will be perfect when our product is released", but not so easy to say "we are currently being delayed, because we are negotiating DRM issues with publishers."
Therefore, my bet is that most of the delay is caused by the insistance of reader companies to get the blessing of the publishers, and the fear of the publishers from easily accessible books.