Speaking in an interview on ESPN Radio's "The Dan Patrick Show", Stern said the league has to abide by rules mandating a one-game suspension if a player leaves the bench during an altercation.
"Our players have to learn that they can't leave the bench and move 20 feet down the line, wherever it is, and be subject to all of the possible things that can happen," Stern said Wednesday. "That's why it's a red-letter rule."
Stoudemire and Diaw both received the mandatory one-game suspension for leaving the bench area following the flagrant foul by San Antonio's Robert Horry on Steve Nash in the waning seconds of Monday night's Game 4, which tied the series at two games apiece. Horry got a two-game suspension for what Nash called "a quality hip-check" and for a forearm to Raja Bell in the subsequent scrum.
Horry said Nash over-dramatized the bump when he went flying into the scorer's table.
"I thought I'd just bump him a little bit," Horry said. "As you know, the great acting skills Steve has, when he hit the floor, then flopped and did 'Oh, I'm dying here' -- it happens. I really wasn't trying to hurt him. I had no malicious intent to hurt Steve. I like Steve. He's a good person."
Stern said the NBA conducted one of its most thorough investigations into the matter, repeatedly reviewing the tape of the incident in question.
"You look at all the angles. You decide what to do with respect to Robert Horry. So you talk to people, see what happened. You try to do it in some full way," he said.
Stern said he didn't think the league was too severe in its punishment. He said Stoudemire and Diaw making a move toward the court melee contributed to the severity of the penalty. He added that there are no provisions for a special exception based on the pedigree of the player.
"So these players took themselves out of the game, except for the exception that you would like is if it's a franchise player as opposed to a scrub who goes out, we should add some factor that allows us to do that. OK, I mean, I'm going to put that to the owners. This subject has not been raised in 10 years," he said.
Stern took exception to criticism from ESPN Radio's Patrick that the suspension of the Suns' players unjustly benefits a Spurs team that apparently instigated the foul.
"To listen to the palaver that Robert Horry changed the series is just silly," Stern said. "What changed the series is Amare and Boris ran out onto the court and they either forgot about it or they couldn't control themselves. I don't know which one. And there wasn't an assistant coach there, one of six, to restrain them. OK, so now either we have to have new rules, put up a fence, or hire more assistant coaches."
In Game 5 Wednesday, the Spurs moved within one win of the Western Conference finals with an 88-85 victory in Phoenix. San Antonio can close out the best-of-seven series with a Game 6 victory Friday night at home.
Spurs forward Bruce Bowen, who has become a nemesis to Phoenix fans, sank a tiebreaking 3-pointer with 36 seconds to play. That gave the Spurs their first lead since the game's opening six minutes. Bowen was labeled a dirty player by Stoudemire early in the series and the subject of taunts all night from the Phoenix crowd.
"After all the things I was hearing from the sidelines it was great," Bowen said. "The people were calling me choice names I had never heard before."
Information from The Associated Press was used in this report.