I'm not the first writer to compare producing a book with producing a baby. I once heard Dan Simmons say that publishing a book was like putting your baby into a carriage and parking it on the sidewalk for passersby (in this case, book reviewers) to revile it and call it names.
A big difference is that babies generally take nine months to produce while books can take anywhere from several weeks to many long years. When you are an aspiring author with a finished manuscript, your “baby” is not only unborn, it is still highly mutable. If you change your mind about a character or a plot point, or you think of something you want (or even need) to add, you can do it. Thanks to the wonders of word processing, the only difficulty in making changes is keeping track of versions.
But once you publish, either traditionally publish or self-publish, the baby is out there for all to see. The other day I had a sudden insight into a situation in Shades of Empire that would be helped by adding a mention of something about the protagonist's motivation. Immediately, it occurred to me that I could not easily add that in as I have already published the book!
Now of course, with ebooks, I could edit and reload the book, but for anything less than mortifying mistakes, that way lies madness. What if you fix or add one thing and then think of something else? When would it stop? Besides, if you're like me and you rely on a conversion house to produce the Kindle and epub versions, you might need to pay for every edit. There are also folks who make the argument that editing a story post-publication is unfair to reviewers whose comments may no longer apply. Really, you shouldn't be publishing a book unless it's “done.”
That said, there are times when the ease of digital changes come in handy. A major part of today's ebookstore “stock” consists of yesterday's books, the backlists of published authors. In some cases, the publisher has (or negotiates) ebook rights, and in others the author self-publishes his or her backlist. But in either instance, some of these books are decades old. YA fantasy author Diane Duane recently decided to republish her 1980's fantasy So You want to Be a Wizard as an ebook, but first she updated it in a bunch of ways. She has named the new version the New Millenium Edition to make it clear there is a difference.
Again, there are trade-offs. As this post on Teleread points out, people get miffed at the idea that they have to pay for the book again to get the “director's cut.” On the other hand, the new edition might offer a better chance of reaching new readers. As always, new technology makes work easier and faster to do, but that doesn't mean it's always a good idea to use it.