What difference does it make? They wouldn't lower their rates and a zillion people are still on FB so advertisers are going to buy the slots regardless. "Ad targeting" is not something that people outside of the niche of advertising economics care about.
Well, I understand that Facebook will try to extract as much value from advertisers as possible as well, testing the price they're willing to pay based on the conversions that advertiser hopefully are tracking accurately.
I more was curious of whether the history cleared with Clear History are primary markers for ad targeting or if other data is used, and in reality if enough users don't clear their data but have similar data fingerprints (the non-Clear History data) then Facebook could still present assumptions to target by for those who do clear their history regularly, e.g. it will be a moot point up until say 40% of people regularly are clearing their history and therefore can no longer accurately enough make those assumptions.
