Earlier quoted context omitted.
Tracking is necessary for the advertising economy to control bad behavior on the part of publishers and advertisers, not just to serve targeted ads. No matter what there would be discrepancies in the numbers (publisher says it sent 75 clicks, advertiser says it got 70) and that breeds mistrust. Participants have a reason to lie. Having multiple third party watch the whole thing helps them trust each other.
This has been possible before. Google was built around content based advertising. Also, maybe click-through rates are not that important? Maybe exposure is a more decisive metric? As a side-effect, we may reduce social bubble effects and maybe even return to a shared reality? (Many of the unwanted effects of the Web are really due to targeted advertising and its consequences.)
For instance, there are discontents around Nielsen (they've had scandals in India, and I infuriate people in the TV industry with the suggestion that a Nielsen home got bribed to blast MTV in an empty room) but the participants believe in Nielsen: people know probability-based sampling basically works.