Thing is even the traditionally published authors I know need to do all of that to sell more than a couple of hundred copies and receive something reasonable financially in return. Many do the school visits, library visits, bookshop visits, websites, twitter, forums, facebook etc
It is very possible to only sell one hundred copies with a traditional publisher.
Only if the traditionally published authors you know are selling their books to small presses (or vanity presses masquerading as traditional publishers of which there are probably more than the legitimate kind these days, because there is a lot of money to be had preying on aspiring writers).
If you sell your book to a major publishing house and you sit home and do zero self-promotion, and the book is a total flop by industry standards, you will still have sold a few thousand copies. Self-published or with a small press, you generally have to work very hard indeed at self-promotion to sell that many copies.
There is also one financial consideration to self publishing ebooks compared to trad publishing that everyone seems to overlook. When you epublish yourself, your book what ever it is, is out there for life.
This is the greatest advantage of self-publishing, and I don't think anyone is overlooking it, but you still have to go out and work to make sure that people know the book is
there. Sitting there in 4,000,000th place on amazon is not going to bring in any sales, even if the book is there for a hundred years.
I'm in the process of self-publishing my back-list. I could definitely use some money coming in, but I am also eager to get the books out there into the world again, because there was no chance of my publisher reprinting them after all of these years, and essentially I want those books to live on and not disappear during my lifetime.
As for sales, as a traditionally published author I already have a modest fan base, and I
hope that those who have already read these books will recommend them to others -- or want to buy nice new trade paperbacks to replace their yellowing mass market editions. But also I think I am wiser than I was even a few years ago, and intend to do much more to promote my books than I ever did before. (Including letting those who have liked my books in the past know about the new editions as they come out.) A lot of us have to get over the idea that it is somehow crass to bring our books to the attention of other people, and so we just sit there and hope that somehow the word will get out in spite of our shying away from spreading the word ourselves.
I think I've pretty much got over that idea now.