There are some like M.J. Rose and Brandon Sanderson who started out self-publishing or podcasting or something and then got publishing contracts. Numerous others who do very well as blog authors and have parlayed those into book deals---or have remained as income-generating bloggers. And at least one (Jim Munroe) who started with a traditional contract and then went indie afterward.
Personally, I think the next big internet success story will be the one who offers the ebook for free with the catch that the movie rights cost a million dollars, and then gets a taker on it
