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Many AdSense publishers optimize for clickthrough rates (e.g., by extreme "blending," placing several ads above the fold, using AdSense in lefthand navigation bars, etc.), but such optimization doesn't necessarily benefit advertisers--which means the publishers may be "smartpriced" or advertisers may add the non-performing publishers' domains to their blocking filters.
Now a businessman becomes the mayor and pushes through a rule that says you can have a billboard every 10 feet. As the billboards go up it is likely that the cost for that space will go down. Eventually they might even get blank billboards or, can you believe, ads for dating services and 'free widgets'.