Macsuer,
You have stated the obvious as we all know that iBook and iBooks Author is mac only.
That isn't even the main concern. I don't mind creating and delivering on my mac at all, but its about those that can access the books.
You make a point that makes no sense.
"With iOS 8.4, iBooks Author created books can now be used on an iPhone opening up another large audience.
But I'm afraid expecting these books to be available on PC's is missing the point and aim of the app."
If the point is to reach a larger audience it makes ALL the sense in the world to open an iBooks Store for the PC. But you state in the first sentence there its about reaching a larger audience, then state there is no reason to open it to PCs. Well opening it to PCs would open it to a larger audience.
No it doesn't drive hardware sales directly, but it makes your authors happier, it makes the purchaser of books happier, it exposes more people to the mac experience, which can indeed sell more hardware. Just like the halo effect that the iPod had, and it puts money in Apples pocket, (not that they need it) it puts money in the authors pockets who are using mac hardware. You also assume you want them to repurchase mac hardware.
So for me as a teacher I have no incentive to use the iBook store, iBooks Author really (the ePub format is anemic), or expose my students to the mac experience and will have to use other alternatives. So Apple loses all around there, and keeps a fairly small group of people happy.
As I have done a lot of looking around during this adventure, the authors as a whole are not selling on iBooks, but other platforms. If that trend continues it will give them no incentive to make books for iBooks. Apple has frozen itself out of the education market for me, and I have to assume many others as I have mixed platform students. To dismiss the education sector is short sighted. For what its worth I live and work in India, a growing market if there ever was one.
You contradict yourself with your argument and it makes no sense to keep the largest segment of the population out of being able to purchase iBA created books regardless of how you try to spin it.