I'd argue that those most likely to use Adblock and similar addons are those least likely to ever click on them. My (quite anecdotal) observation is that many less technologically minded users notice and click on ads, while more experienced users see only the content and grow tired of flashing in their peripheral vision.

That hypothesis extends partially to why Hacker News and similar are so different from, for example, the much messier layout of cnn.com.