Most ad placement services, such as Adsense, use some combination of keywords on the current page and the nature of the website itself in order to select the ads that do (and perhaps more importantly) do not appear on a given webpage.
Which is why the placement of the following two ads on the same page caught my attention:
I understand why ad #1 is there. The site I was looking at hosts a large number of Christian/Evangelical blogs. The individual blog I was reading focuses on issues of evangelical Christianity.
In the process of doing my work I wander around many website and I have only seen ad #2 on that particular website.
So the question is -- is the service that selects those ads for that page "broken"/"made a mistake" or -- do they know something about the typical reader of that site that I don't know?