One reason to justify Google's cut is that on an advertising deal where the Advertiser gets billed for each click (CPC) on his link on someone else website, hav

One reason to justify Google's cut is that on an advertising deal where the Advertiser gets billed for each click (CPC) on his link on someone else website, having a reliable third party to count the clicks is very important. Click fraud is what makes Tier 2 CPC networks really risky for advertisers even if CPC are much lower than Tier 1 (Adwords, Bing). Regarding your Adsense example, was there not a mention like "Ads by Google," "Sponsored Links," or the AdChoices icon ? In that case, it makes clear that it's not a natural link.