I don't think it is a bias either. Since the query was "webmaster world" I would think what links that do show up are less keyword based and more popularity based.
General theme? Pretty much the sections shown are the ones that are the largest, most active, and the most heavily linked to. General links to the WebmasterWorld home I suspect are heavily Google related so that is what you will see in the site links.
But as always with Google...who the hell knows for sure anymore!