Playing an 11 man roster in these playoffs would have been a disaster. One of Doc's biggest knocks over the years is that he is not good with rotations. Until they consolidated the roster down to the big 3, etc., he was not considered a particularly good coach. However, with the shortened roster, the team has succeeded in large part b/c we have a big dropoff in talent/performance after the the top 6 or 7, and we are only playing 8. Even JVG highlighted this and says it is best for the team.
I don't wan't Marquis or Sheldon getting minutes because it'd be taking away from a better player. Doc has told them that they will be needed these playoffs, to be ready, and that they will play an important role. At no point has he destroyed their confidence. Just look at Nate, the guy is excited and the first to wave a towel.
On the topic of Pierce's play, he blew it, but you're right that defenders came over. This has been one of my only knocks on Davis these playoffs in that he brings his defender too close to other players with the ball, etc. He's not necessarily alone in doing that, but he's probably the worst.