This might be a little out of date, but the breakdown is something like 40% retailer, 10% distribution, 10% print, 5-10% author, 10% editorial, 20% profit. On future print runs the publisher gets more profit of course. NB the retailer takes most of the profit. For ebooks the situation is worse in that Amazon takes 70% unless you choose to sell exclusively, but at least canny authors can bypass the publisher. You can see then why publishers are hostile to ebooks, for them it is an even worse deal and they lose control to a predatory retailer (Amazon).

5000 sales is larger than most first print runs, a minority of books are bestsellers and sell hundreds of thousands, the majority sell just a few thousand and make very little profit if anything, this is why publishers offer an advance set against future royalties.

There is still a vestigial authority to a printed book (someone other than the author liked this) and a stigma attached to self publishing, so there is some value still to being published on paper, because the main benefit to most authors is reputational, not monetary. It will be interesting to see if that changes with ebooks. However, like print newspapers, mass-market print books are dead, they were always on thin margins but are now unsustainable. This will take a decade or two to work out, but it will happen.