Can anyone explain why it's the ad buyers that lose out in this case, not the ad network? Surely it makes way more sense for the ad networks to bare the financial responsibility of preventing ad fraud and not the ad buyer? (The ad equivalent of a money-back-guarantee) How is an ad buyer ever supposed to make an informed decision about how susceptible their chosen ad vendor is to fraud?
As long as you're hitting your target ROI than advertising on still makes sense.