Vamm; I would never suggest that they are. But they are cheap. And domain names don't HAVE to include you niche key words to be successful. A .com domain with a six-letter made up name, which you could build into a brand (Or not) costs a few dollars a year.
But the cost of web publishing is negligeable compared with print, and once established, the marginal cost of another 1,000,000 pages, set up for SEs and never visited by human beings, is virtually zero.
That's my point.