Google are putting more rank into "brand" sites. They confirmed this a while back. People have challenged what a "brand" is but not with much reply.
They probably human manipulate the rankings of high profile sites. They did this to try and get rid of more spam sites. You know the story, you do a search for a well known company and are confronted with 50 affiliate sites instead.
http://www.seobook.com/google-branding