Re: The coaches or the players...
The great coaches develop schemes that put their best players in the best scenarios to be successful. That is a HUGE key when talking about a subject like this. They surround themselves w/ players that will fit into their plans and players who can do the things he will ask of them, and they in turn perform at a high level because they are the right person for the job. As opposed to another GREAT player who could have been chosen but wasnt because his skills didnt fit well into a particular teams system.
by that logic, you can make a good case for the coaches being the big reason.