Well, there's nothing to say that eBay's research lab was using these horrible PPC ads in their tests. In fact, I would guess that they had to hold the landing

Well, there's nothing to say that eBay's research lab was using these horrible PPC ads in their tests. In fact, I would guess that they had to hold the landing page as a constant (e.g. homepage when "ebay" was the keyword), or otherwise account for that variable in the study design. For instance, the study notes that, for one test, they simply turned off their PPC campaigns for one geo and compared results to others. So, presumably, even if they were using their horrible PPC ads during this test, they would have been equally horrible across geos.