The renewal rate on one year registrations in .COM is down around 54%. There's a lot of coupon driven registration trends and probably some of these domain names were one year wonders rather than long term (multi-year) sites.
If you install the Google Publisher Toolbar extension for Chrome, you can get more information and block ads from there too. Which is convenient, except that I seem to see different ads in Chrome than I do in Firefox or Safari. Not sure why that is.