The AP is reporting that eBay is back running advertising through Google. Turns out my hypothesis must have been at least partly wrong. My latest explanation, for whatever it's worth, is that the pricing is still better on the Tier 2 networks, but that they don't have enough traffic at this point to satisfy eBay's voracious appetite.
Google's too big to ignore, apparently. (Perhaps that point was obvious to everyone except me – and eBay.) eBay's spokesman was quoted as saying that they were still pulling back a "significant" part of their spend from AdWords, but that smells like so much PR spin. Absent any real definition of "significant", chalk up a win for Google.