stay away from the
iBook Store completely and buy all ebooks from some other book store.
The iBooks store allows their own private extensions to the epub standard that are not even in ePub 3 spec. They are trying the same "embrace and extend" approach to breaking the standard as Microsoft used to try with Java. Nor do they provide a Desktop version of iBooks so that people can read at the Desktop.
Apple should be ashamed of itself! Please do not give them any iBooks business!
Nobody seems to be working on removing DRM from iBooks store ebooks. If you need a DRM-free ebook, do NOT buy anything from iBook store.