Indeed - do a search for anything Google determines to be non-commercial (like "retrovirus", "contract for difference" or "banana") and they simply hand you off to Wikipedia. It's Wikipedia, and not Google, who really own the show when it comes to collating the world's knowledge.
Now that's a bit conspiratorial. Probably a majority of people searching for "retrovirus" clicked the Wikipedia article link. Google figured this out, and started listing it first. Nothing beyond Wikipedia fulfilling its role.
