It is worth noting that you can't export to standard EPUB3 file format, only to PDF. PDF is obviously non-interactive, while the EPUB3 standard would allow for most if not all of the interactive elements that can be created with iBooks Author.
Many argue that they are in their right to put that EULA, and that others have done it before (Microsoft's Word, for example). And they are absolutely right.
That does not mean, however, that this isn't a very greedy move - many even describe it as 'evil' - and just like it happened with Microsoft in the past, I can totally understand why.
Having a right to do something is not incompatible with being greedy or even evil.
A peek into .iba files and a comparison with epub files evidences that Apple deliberately re-designed and implemented features in order to make the ibooks file format incompatible with industry standards. Again, while they are fully in their right to do this, this should be worrying to anyone who appreciates healthy competition and doesn't enjoy Microsoft-like monopolies. Ironically, this has happened with Apple being a member of the International Digital Publishing Forum, who manage the EPUB standard.
(This really smells like embrace-extend-extinguish to me.)
Perhaps what bugs me the most is that in spite of all this, no-one (AFAIK) has taken the time to provide an alternative tool which allows to create interactive ePub documents just as easily. It seems to me that Apple was first to do this "properly" (as it usually happens), and in this case there is no technical reason why it could not have been created 1 or 2 years ago by other industry leaders - I have used iBooks Author and it isn't much more than a glorified presentation editor.