The trusted nodes are where the "51% proof" comes from. Another name for them would be the central authority.
In theory anyone can be one if they meet the networks requirements, but CH/RS has ducked every time anyone asked what those are.
My guess is the 'network requirements' are that every second block has to be signed by some king of magic private key. Of course that would be terrible design as the key will leak sooner or later but I can't think of any other way of getting trusted super nodes to contribute to the block chain in the way SC2 seems to have done.