I used to be a platinum powerseller on eBay ($150,000/mo in revenue). I don't know if the metrics you have are necessarily indicative of Amazon ranking over eBay. I can tell you this, their platform was completely different when I would sell on both. For instance, Amazon ALWAYS had a static page while I would create a page on eBay that would only last 30 days. If you take the scenario, Amazon has a lot more time to have links pointing to individual pages whereby ebay doesn't. EBay is freakin awesome and yet I hate them. BUT they do have a MASSIVE repeat buyer community. I have sold on both and bought on both.
It comes down to how many quality links point to that particular page; whether on Amazon or eBay.