Baldur Bjarnason does a fantastic job dissecting the innards of Apple's new iBooks 2.0 Textbook format.
He writes the following comment on Asymco:
Most of the output of iBooks Author is non-standard CSS and non-standard interactive widgets. I've written about the CSS… And I'm planning on writing about the widgets later today, but the short version is this:
The interactive widgets are a combination of custom object tags and data- attributes that are then rendered using proprietary code in iBooks 2.0. Any browser or ePub reading system that wanted to implement support for those widgets would have to reverse engineer them first.
So, iBooks Author is not an HTML5 authoring tool, its output is decidedly non-standard, and it's far from being cross-platform. It's a proprietary tool for creating proprietary files.