You know the difference between the Celtics and the Mavs. The Celtics were a mature team that was injured and had a lousy bench. The Mavs were a mature team that was healthy and had a bench.
Kidd - 38 years old
Dirk - 32
Terry - 33
Peja - 33
Marion - 33
Cardinal - 34
But they had some younger guys like Barea, Beaubois, Chandler, Brewer and Stevenson that produced.
Dallas overcame their injury to Beaubois and Butler because of quality depth. Boston couldn't overcome their injuries to Perk or the O'Neals or Daniels because of poor depth and because the injuries were concentrated in one position, the center position.
Ultimately, mature teams thrive in the playoffs because of a slower pace, tighter defenses, more physical play and the need to play intelligently. The Celtics would have been fine if healthy. They were not healthy. They have another run but they need a deep bench and health like they had in 2008 because, like it or not, in most team sports, the champions tend to be the ones that have talent and the most health.