The Internet and advances in technology have made huge leaps since the days of Benjamin Franklin and Mark Twain, and even John Grisham and James Redfield. These were all self-published authors in the purest sense of the word. They took all the risk involved in the writing, editing, design, printing, and distribution of their books—and reaped the rewards.
There are many reasons for self-publishing—or going the more direct route than traditional publishing requires: writing query letters, finding an agent, finding a publisher, and negotiating contracts. Perhaps an author wishes to have a more timely publication because of a recent event, or just wants to be in control of the process and receive full price for their books when sold. (That gets into a discussion of royalties … a topic for another blog.)