I think Google is quietly increasing the weight of "TrustRank". I think they are manually giving "authority" to a limited number of sites and letting those sites give it to others sites via links.
It's a hidden shadow of the "PageRank" system. The major difference is the manual component, the hand selection of sites of which Google approves.
One of my sites got one link from a deep page on a leftist blog and Google referrals immediately doubled. That shows the leftist site has a lot of authority, a lot more than is represented by their PageRank.