Because you're exaggerating what actually happened. They slung their arms at each other. No way on Earth is what happened there even comparable to Artest and Posey. No way. Plus, remember that Stu Jackson makes decisions based on premeditation. Artest's incident clearly showed that. Posey's was borderline at best. Kwame and Diaw were tussling after a rebound. He did NOT get laid out by any means.
Walton also did not mug Tim Thomas. All he hit was his arm while going for a shot.
Thomas has a sprained MCL by the way. He's questionable for the rest of the series. His teammate did it, thank God.