Self-publishing does not count as real publishing, and PoD and self-publishing are not the same thing. PoD is a technology. Self-publishing long pre-dates that technology and can be done by PoD or traditional printing.

Edit: If someone really did want to go the self-pub route, I've read that lulu.com is the best choice. But my knowledge of that process is pretty limited.

One is the comic book industry. Most new writers and artists start with a low print run self published book that they can shop around to people in the industry at conventions.

The second is the roleplaying industry where there is similar shopping around at conventions.

People who do seminars sometimes self-publish to sell their books "at the back of the room." This is a valid use for it. Poets self-publish out of necessity since getting poetry published in book form is almost impossible these days. People self-publish books that are of interest in a very limited area such as family or church histories. Writers who consider themselves hobbyists sometimes self-publish just for the satisfaction of seeing their work in print.