I think another reason the DF advertising model is so successful, for both the publisher and the advertiser, is that the advertisements don't distract from the publisher's content. And in this case it plays really well with the primary means of publication for DF, RSS.

Consider "traditional media": radio, television, and print. Yeah, we all love to hate commercials, etc.

But compare it to the Internet, which is a complete cesspool. I use my hometown newspaper as a example (http://www.ajc.com/). Many websites are completely unreadable, and/or require a supercomputer to fully render and execute the CSS/JS. And I believe it's fairly common knowledge now that these types of advertisements are hugely ineffective for the advertiser.