Apple is the only major online bookseller that actually sells content on the iPhone and iPad. Amazon, B&N and Kobo all make readers visit their websites and sync the content, which is a barrier for mainstream adoption. This summer a new version of iOS will be released and it will add a bunch of new content to iBooks.
The publishing industry has been embracing audiobooks in a big way. In 2007 a paltry 3,073 audiobook titles were produced and this figure rose exponentially to over 12,000 published in 2011. In 2013 over 20,000 audio editions were released and in 2014 over 35,000.
Apple has an extensive audiobook selection in the iTunes store and the source all of their content from Audible. This summer, the audiobook experience will be changing as it will be fully implemented into the iBooks app. This will obviously be shift the buying experience from iTunes into the iBookstore.
The second major change is that iPhone owners will have the chance to open e-books made with iBooks Author. In the past, these titles were only available on the iPad and often included audio, video and widgets.
It really looks like the iBooks app is going to be a bit more intuitive for iPhones and to a lesser extent iPads. I know many readers that are going to be excited about these changes.