[Uberphallus]

Not a design/advertising guy, but often times I think it's to be able to display an ad at the bottom without the user to fully read the article, and without putting it ahead of the article (which is ugly IMO).

Here though I don't think it's the case.

[imsnif]

There are no ads on my blog and will never be. That's a promise :)

[mongol]

That is why you are a poor dev :-)

[PaulHoule]

Ads on dev blogs pay peanuts, if that. It's a way to stay poor.