Re: Published authors and percentage income
The big difference between trade publishing and self-publishing is that with the former, you get a lump sum (in installments) which is yours to keep regardless of how well your books do. With the latter, in order to get an equivalent quality product you generally need to invest money upfront (cover, ISBN, proofreading, etc) and there is no guarantee you will recoup that investment, never mind turn a profit. Some do, but a great many do not.
For those with entrepreneurial flair and either money to invest or the necessary skills, self-publishing can be a very attractive option. For those who just want to write and would rather leave the rest of the process to professionals, a conventional book deal may well be preferable.
P.S. Do not confuse self-publishing with e-publishing. Most trade publishers now e-publish (some imprints like Carina are ebook-only), and some self-publishing packages include print options. The medium is separate from the business aspect.