Popovich could easily accomplish his stated goal of resting players by staggering the games in which they sit out. For example, Manu and Duncan could have rested against Orlando, and Parker and Green against Miami.
There are two reasons I can think of that Pop would sit all the starters at once.
1. He knows it will piss off the media and the league, and he wants to shove it at them. (applause)
2. He wants to give the bench the experience of having full responsibility of the game on their hands, and use this as a team-building opportunity. (appluase)
The fact that Pop sits all the guys at once tells me that this is not completely about "rest", even though most of it is. There is also another agenda or consideration by Popovich here that we aren't fully aware of.
When the Spurs lose...it makes Baby Jesus cry