The author of the hyperblog:
Gennadi Bedjanian of Vancouver, BC, Canada.
I grew up with the Internet so hypertext is where I naturally occur. I even saw physical hypertext in Tokyo. More details are probably irrelevant here. I'm not even putting my distracting face on this page.
This is all about Hypertext.
email: 
EBOOKS AND BOOKS ARE ESSENTIALLY DIFFERENT
One: a nonsensical double metaphor
Do you know the definition of ebook? It doesn't seem to exist. "A book in electronic format" is nonsense. A book cannot be in electronic format because a book is made of paper. A text can be, but the book and the text are not the same. A book is a container of text. And the composite of paper and ink is a carrier of text. If sheets of paper carrying a text are not bound, there is no book.
Book is a container of text.
So, we have several different things: a text as an information entity that can exist in different forms, sheets of paper as the medium carrying the text, and the book itself as "A set of written, printed, or blank pages fastened along one side and encased between protective covers" (a dictionary definition). Now think about this: Can "a set of written... etc." be in "electronic format"?
It is our propensity for metaphoric transfer that leads us to confusion. Container with its content becomes content, then content transforms back into another container with seemingly the same content, and there we have an ebook that looks very much like a book, which it is not.
Two: the missing guts
And yet, we doggedly call them "ebooks". Why? Because ebook is very similar to book. This similarity helps to understand the constituent parts of an ebook.
As a physical entity, a book is a bound set of sheets of paper, an ebook is a file.
Pages with coded text in a book (an alphabet is a code) correspond to computer code contained in the file of an ebook.
Now get ready to make an intellectual leap into the non-physical. The raison d'être, or the reason for the existence, of the book is text. Text is the guts of a book. The guts of an ebook is... hypertext. "Nobody knows it", as B K S Iyengar likes to repeat.
Definition of ebook
Now we are ready for the definition of ebook:
Ebook is a container of hypertext.
Confusion is gone, and many things find their places. Thus, the PDF format is good for printing purposes, but it supports only almost flat hypertext, and therefore makes poor ebooks. PDF ebooks are electronic copies of books, an intermediate stage between books and ebooks.
HTML is the most multi-dimensional mass format, therefore it should be used for ebooks. Ebooks need standard shells to contain HTML pages. XML-based ebooks are even better, but there seem to be no authoring tools for them in the foreseeable future. Again, it must support real hypertext, so print-oriented markup languages are of a very limited value.
The analogy between books and ebooks is very productive. As another example of it, there are hard cover and paperback books, in a similar way we may distinguish between ebooks for computers and for mobile devices. In other words the same ebook need not have to be readable on both computer and smartphone. It may have different editions.