No, I'm assuming that they could just buy ads with the same ROI in many places. For instance, if Facebook ads cost 20 cents cpm, but they earn 40 cents, then their ROI is 2x. I would assume they would have no trouble finding ads elsewhere with a 2x ROI. In fact, I'd be surprised if the market didn't function to make their ads be a 2x ROI at MySpace, Bebo, Hi5, and maybe Digg, Reddit, etc.
Spotting market inefficiencies like that should be really hard to do, considering that all of the mortgage brokers, for instance, already know their ROI on various sites, and the market will make it roughly equal everywhere over time.