It's incremental now. At this point, they accomplish the same thing. That's the job of a book no matter what the medium is. But while the medium is not important, e-books do offer many advantages over print books. Not the least of which is cost of production and preserving a natural resource.
Web publishing is destructive because there is no editorial control.
There will always be bad epublished books and good ones. A lot of people don't know there are different types of e-publishers. Some will publish anything at all for a buck and some are set up in much the way any publishing house is. Including me, about nine. I wrote and rewrote and rewrote the book, then it goes to an acquisitions editor who either accepts or rejects it.