The TPCK model

Technology:  The tool itself is based in technology.  iBooks takes a regular book and infuses technology to your everyday book.
Pedagogy:  At its core iBooks is still a traditional textbook but it allows for more 21st Century content to expand comprehension and interactivity.
Content:  iBooks do not change the content of the textbook but instead allows you to enhance the learning experience.

Knowledge:  The additional elements that can be added through iBooks and iAuthor enhance the experience and the information that can be retained from the instruction.