I am too curious about this strategy. You can find Google's point of view on smart pricing at this link. But this point of view is to satisfy marketers, not the publishers. My questions is. Have you ever observed smart pricing to your earnings? AND How do you think Google determines this keeping in mind the Google's explanation in above mentioned link.
It is all a matter of history, demand, supply and competition. Their aim is to reach a balance between meeting the demands of publishers and marketers.