That's a distinction you are making - that books cannot or should not be updated, whilst web pages can/should be. It's no longer intrinsic to the nature of a book as a digital text.
Perhaps a list of heads-of-state is a silly example to use, but a text-book may be a better example - in a digital world it may be a reasonable expectation that a text-book would be 'correct', and so receiving updates would be appropriate. Or a particle physics data-sheet, where an updated value for the mass of a particle could be included.
Of course this should be consensual - "The publisher has provided an update to this text. Please accept, reject or review the changes", and it would be great if e-books and readers had a mechanism to scroll back and forward through editions (but perhaps that is a pipe-dream).
> I have old astronomy books that indicate the visual appearance of Mars changes due to seasonal vegetation! This was obviously updated in later editions; the old edition remains as an important historical record of what we once thought.
That's pretty much what I said in my comment. Sometimes the historical context is important, valuable or interesting.