When the literati talks about books, they talk about them as if they were alive, morphing and changing with each reader as they apply their own interpretations and experiences with the book. That's not what I want to talk about however. When people finally see print, there's a sense of finality, of tangibility, of permanence. Once you write down something, you can't take it back. Or can you?
Online publishing is easier to edit that printed books. There's no plates or inks or paper stock to worry about in the former. But that doesn't mean the latter isn't any more morphic. Just as George Lucas strove to edit and change his Star Wars series, I think such a feat is possible when it comes to books, and it's been done before.
One way is to slightly alter and change the text with each edition. Michael Moorcock is guilty of this (and that's why you'll read several slightly different versions of the Elric story) and one of today's more mainstream titles, Raymond E. Feist's Magician: Apprentice and Magician: Master, certainly fits this revisionist mold (Magician used to be one book you know, not two).
Then there are the short stories or novellas that get blown up into whole novels. And that's not necessarily a bad thing. I mean Orson Scott Card outdid himself with the Ender's Game short story but the novel is equally as astounding. And he's not the only one who has succeeded in such a feat. We have the likes of Greg Bear for example or in mainstream fantasy, Robert Jordan.
A slightly different take would be the reissues of old publications. Like when H.P. Lovecraft's works were re-released by Del Rey, a variety of well-known authors wrote the introduction, such as Neil Gaiman. The actual text hasn't changed but there's some perceived "extra value" when you include features such as a new introduction, a new foreword, or even a study guide.
It's most evident, however, in nonfiction books. References books, text books, and history books are prime examples of publications that get continually revised and re-released on a regular basis to the point that you might not want to keep old copies of the books because they're outdated. In fiction, you'd treasure these "unmodified" manuscripts but in the case of nonfiction, the sooner they're replaced, the better.
Books have a feeling of permanence yet the text they contain are still susceptible to the winds of change. Writing changes, writing evolves, sometimes for the better, sometimes for the worse.