I think they are trying to say a asignificant number of people go to the site by typping in the url rather tahn clicking on the ad. The ad itself increase the exposure of the product/service they are advertising.
Regarding this article, I would comment that I myself use to avoid clicking on ads that were because of several ads use to install spyware and other softwares which makes my pc slow, and for that I would blame PPM, anyways nowadays when I see any interesting ad I do click on it.