Joe Konrath, the Pied Piper of self-publishing, asks this question of those authors who still defend traditional ("legacy") publishing houses and dismiss self-publishing. And he answers it here, in a passionate and persuasive defense of the self-publishing revolution.
If you are a writer, and you wonder what is all the recent fuss concerning self-publishing ebooks, rather than seeking a traditional agent and publisher, then Joe is the guy you should read -- and this blog post is a great place to begin. After you do, check previous posts on his blog; they're eye-openers.
For similar reasons, two other must-read blogs for authors are Robin Sullivan's "Write to Publish," and Dean Wesley Smith's. They'll introduce you to an amazing and exciting new world for authors.