I think Steve leaving CEO to being only the Chairman of the Board and everyone knowing that he is probably contacted on a daily basis on all major decisions as well as getting updates on the company is not really the test of how Apple will do without Steve. I think the market assumes that (a) he still has tremendous influence in the company and (b) if something were to happen that he didn't like (like Apple buying Facebook with some of that cash it has lying around doing nothing), that Steve would veto that action and possibly re-establish himself as CEO.