They do the best job of bringing in the role players that fits their style better then any other team.
Pop then asks players to do what they can instead of trying to make them do what they can't. (think the Celtics early this season having Terry play the Ray Allen role)
This in spades.
Pop builds systems around his talent - and his front office hits a higher percentage of its talent choices than any other team in the league.
He's also a master of managing minutes for his aging stars, and they put together depth that allows them to do that effectively.
As noted above, they also are very astute in cutting bait with players who don't fit their model - something the Celtics have struggled with under Ainge.
Anyone think Pop would have clung this long to Rondo? Of course not.
Ask yourself this: Would the Spurs draft the Purduo? Would the Spurs draft Fab Melo? Not a chance.
The Spurs don't hit all of them. No one does. But they certainly are better at what they do than Ainge and Doc are.