Google News leaning leftward?

How is it that Google News considers Democratic Underground a news site … but not Free Republic?
Here’s what you get when you search for “democrat OR republican” using the Democratic Underground as the source. Here’s the same search with Free Republic as the source.
Just asking.

UPDATE: Looks like my chance discovery turned out to be timely. Michelle Malkin’s got a budding roundup of posts on Google’s apparent bias. Amy Ridenour’s speculation about Google’s screening algorithms sounds plausible to me, but I don’t forsee Google letting us in on anything revealing about their search algorithms. Ater all, that’s what made them so popular as a search engine to begin with, and their popularity drives their ad revenues.
Mick Stockinger at Uncorrelated observes that algorithms don’t conspire to slant the news. Granted. But algorithm writers certainly can. I’m not saying that Google did any such thing … I am saying that Democratic Underground’s presence in Google News’ search results strikes me as a bit odd given Free Republic’s absence.