I have no expertise in this, but I don't see why anyone would pay for banner ads for more than pennies on the dollar if tracking is an option.
Wouldn't removing tracking change the economics?
Also, this specific situation seems like a good candidate for regulation, which removes the need for businesses to be ethical of their own accord.
On the other hand, it can be that people detected the change on their results metrics, and decided to increase their spending because of the change. I really don't know how to differentiate this scenario from a normal increase on internet advertising that should naturally happen at the earlier days of a fast growing web. I don't think even Google (that has all the numbers) can tell them apart either.