I find this to be a total joke of a move by Stern
The Spurs have every right to rest THEIR players at their own discretion. The team pays the players and if they feel they need to protect their investment and that it helps them in the long run to give players rest, the NBA shouldn't be able to punish them just because it is a nationally televised game.
Stern feels shown up and this is his retaliation. The reality is, Popovich probably was knowingly provoking Stern with this but the Spurs just came off a brutal stretch of games and because of that, Popovich has a perfectly reasonable case for resting his guys.
Since forever teams (in all sports) have rested players at the end of seasons when play-off spots are securce. To me this is simply an extention of that, protecting players health for more important games. I look forward to April when all teams are resting stars and nothing is done by Stern.