What are the differences between ebook content and physical book content in terms of readability and/or sales? For example, are there any studies regarding the differences between the content that is considered readable on e-readers and content that is considered readable in printed form? Is there anything on the mass appeal of ebooks versus physical books based on their contents? In other words, what do we know about the differences between ebook readers and readers of physical book?
Note: I am not asking about the obvious, like proper file conversion, making sure that chapter/section headings are not separated from the following text, etc.