Exactly. But to "prove" it in the USPTO process, they need that "written down" item. And if it is never "written down" because it is too trivial to write down, then the USPTO' examiner's hand are very much tied.
USPTO has broadened "obvious" recently, partly because of a court ruling that held "A person of ordinary skill is also a person of ordinary creativity, not an automaton" (meaning that the total prior art doesn't need to connect every dot).
