Making a financial success of fiction is (even) harder. Much harder. Generally speaking, I think you need a publisher behind you for fiction, although Amanda Hocking recently managed to bootstrap her way to self-published vampire success.
I agree -- harder to be successful in self-publishing for fiction.
(1) There's less "need" for your book. People aren't saying, "gosh, I wish I could find a book on zombies from Mars attacking Earth. Let's see what my options are!"
(2) You can't differentiate yourself as easily.
(3) To be successful as an author, you need a platform / promotional strategy. It's harder to build that with fiction books (at least until you are well-known). In an "informational" space (business, reference, technical, etc), you can build up a following by starting a business or a website that provides assistance in some area.
