[banannaise]

As Magnus noted in his reasons for stepping down from the match, your first sentence is entirely correct. The 1v1 format of the world championship makes it largely a battle of opponent-specific prep. For a round robin, players generally play their strongest lines and prepare for their opponents' likely responses. For the championship, each player is trying to prepare surprises for the other, and it's largely a battle of who can get their opponent out of prep most effectively without sacrificing advantage, and how effectively you play when out of prep.