A document may be flower, a rock, or a tree. That is, it may bloom for a day and be dead tomorrow, like a newspaper. It may last forever and never change, like Pride and Prejudice or King Lear. Or it may grow and change over the course of a long, if not endless, life like, say, the way a technical manual should, but usually doesn’t.
Just back from JoAnn Hackos’ CMS/DITA conference, where it became clear that even in a conference dedicated to a topic-based authoring methodology, most people are still writing books. Certainly, they are writing them in the form of topics, but then stitching them together into books. The fundamental product is still a book.