This is an interesting article by Mark Coker, founder of ebook distribution company, Smashwords.
Apparently, iBooks will come pre-installed on the Apple's new operating system iOS 8 that they'll be rolling out this Fall 2014.
Prior to iOS 8, readers who wanted to shop the iBooks store were forced to click to the Apple App store, search for the iBooks app, sign in with their email address and password, and then install it.
The absence of a pre-installed app created an inconvenience for readers, which explains why only a fraction of Apple's customer base today has installed the iBooks app. Despite this extra step, Apple's iBooks store has been enormously successful since its launch four years ago. With stores in 51 countries, iBooks has grown to become the world's second largest global seller of ebooks.
We read it a different article that Amazon accounts for 51% of ebook sales and Apple's iBookstoe accounts for 20-25% of ebooks sales.
It will be interesting to watch if this additional visibility of their iBook app pre-load on all new Apple devices will affect ebook sales.