This would make logical sense. BUT! it turns to not be the case. Larger accounts: Pepsi, Johnson&Johnson, Tmobile, etc tend to just take a massive budget and blow it on ads. They don't necessarily care about the ROI or click tracking. They just want to shove banners in front of people's faces before the quarter ends. What is nuts -- is that these large accounts (we used to call it dumb money) are almost all of the ad revenue. Accounts that care about click ROI tend to be low budget -- that is why facebook/google will push these people into self service ad portals.