BookLibrary - only for book
MediaLibrari - support different formats: books, video, music, game - with that was full changed algorithm work with data base, amazon, import/export
Other difference go to Pro versions.
Sorry full difference list very big - you can check that
There are not show last added features description(all require time) - these features you can see at site frontpage
some these features very important for some body some not
e.g. Book Library work with YAZ book servers Media Library not ...