The self published books that achieve the most success have normally (though not always) been professionally edited, formatted and have had covers made by designers. This is a lot of money upfront that the author doesn't have to pay if they go the traditional publishing route.
Authors seem to prefer the traditionally published route; all the indie bestselling author quickly sign up with a top agent and then publisher. It takes a lot of stress off authors and allows them to just be writers. Being traditionally published is also the easiest way to get your book available in bookstores around the world.
Anyway, I wasn't exactly happy with the post when I stumbled across video by John Green where he explains that he wouldn't be where he is today (In a book writing sense) without traditional publishing. So I thought the best thing would be to scrap my post and just let you all watch some John Green instead :P