Personally, I think this battle has already been won by Amazon. The iBookstore is terrible and overpriced. Reading books on a Kindle is superior to reading them on an iPad particularly outside. Kindle app/program is available for practically every platform including IOS devices. Apple’s bookstore is only available for IOS. Not even sure if it is available on the Mac. iBookstore does not have the selection that Amazon does. I could go on.
The Nook, in my opinion, is pretty much irrelevant. Once again, M$ is late to the party.