I have to admit that I was surprised that iBooks was announced for only ioS when it was launched. I didn't think Apple would pass on an opportunity to sell content to their customers. Apple were facing just as much of feature shortfall on OSX as on iOS, so you'd think they would have plugged the hole.
Yesterday Apple gave up the chance to at least lock in their core customers, and that is going to continue to hurt iBooks. If any of Apple customers want to read on this very expensive computer they bought, they're going to go with either B&N or Amazon.
That sitting at your computer and buying ebooks is worth a lot of money. The on-device ebookstores are uniformly crap, so the best time to get and keep a customer is when they're at their keyboard. Apple threw that away. BTW, the PC is still the most popular reading device, so this isn't just the fringe that Apple lost.
iBooks might now be accessible from the web, but it's going to stay a second rate ebookstore.