The new ePub format
Is this meant for school teachers to prepare homework or text in class as the format is now simplified? Are authors trying to get into the iPhone market or is this a niche market?
iBook
The main point of the epub format is to allow authors to create books that can be read on devices other than those produced by Apple, which is not possible with the usual .ibooks format. Also some languages require epub format for acceptance by the ibookstore.
About ePubs created with iBooks Author - Apple Support
The Apple pages app can also produce epub format for a long time already.