How Much Do Authors Make?

I just surfed into the web site of a fav sci-fi author, Robert J. Sawyer, and found a post there on his blog about how much authors make. Very interesting. It’s less than I would have expected, although I would think for the most popular authors, the best-sellers who are pretty much household names (think Stephen King, Michael Crichton, et al) they probably write their own contracts and command a higher percentage. But for the most part it seems to be a relatively modest income.