Having said that, 2009 is a long time ago, and I would like to see this study repeated before drawing conclusions about the current ad landscape.
Without the ability to retarget, advertising revenue at both Facebook and Google would plummet. The majority of conversions for advertisers come from retargeting (behavioral) campaigns. Advertisers run cold traffic campaigns (non behavioral) just to be able to cookie a group of users interested in their niche of product or service. They then show a different set of ads to those that clicked on the initial ad and met some behavioral criteria - for example they read to the bottom of the landing page or watched more than 1/2 of a sales video. It is this second set of ads that results in most conversions from new customers.
So the entire model falls apart if we lose the ability to run retargeting (behavioral) campaigns. Most advertisers lose money on cold traffic campaigns, and make up for it with behavioral campaigns. When behavioral advertising stops, so does non-behavioral, and the whole Facebook and Google house of cards comes crumbling down in a hurry.