It's a good thing that Diggers do not click on ads. If Diggers went to a website en-masse and all of them clicked a CPC advertising link on the way out Google AdWords would run out of inventory and the on line advertising market would crash!
Think about it, a good Digg Effect can generate 60,000+ hits in a matter of hours. Even if those advertising links were only worth $0.25 per click that would be $15K in a matter of hours. Multiply that out by the average number of stories to hit the front page (about 150) and you have $2,250,000 per day!
This would also lead to a massive amount of people trying to spam Digg too but... It would kill the advertising market that so many Diggers tend to despise!