Most professional website that base their income on ad selling will not rely on a Pay Per Click affiliate model, but will have an "Ad Sale Departement" that will sell most advertisment by a cost per Impression model (CPM, Flat Rate).

By professional websites I mean website that will have a team of people working on it that are depending on the ad revenue.

You are correct in saying that those kind of website are a extremly small subset compared to the many small website with a couple of google adsense banners, but are probably the website you read,consume and block the most.