But the possibilities are endless. And the fact that Apple accepts them opens a very large door. It also gives EPUBs on iBooks another competitive advantage over EPUBs on other devices and Kindle books.
(And a tiny aside. I was a bit worried about the accent in the title of my book—Yes, it's "gow-DEE" not "GOW-dy"—but, thankfully, searching on both Gaudí and Gaudi in the iBookstore and iTunes brings up my book.)