It's no more than logical
The one thing a publisher was needed for, the one thing that an author couldn't really do himself, was publishing (printing and binding). He'd be able to hire an editor, if he wanted to, for example, without the use of a publisher. He could even distribute books himself if he wanted to, altough the publisher would make this easier.
Now, the ebooks take the "publishing" out of making books. One can create ebooks directly from the writing software, and distribution doesn't require any effort at all; uploading the book to Amazon and other webstores instantly makes it available to the entire world.
One could wait for parties such as libraries to also skip the publisher step, especially if it's a well-known author of which they already have books.