He should have been punished on the field. If he had been, then there wouldn't have been a judiciary charge in the first place.
There does seem to be a blindspot here, though. The way he behaved really isn't acceptable. I don't know how anyone could say otherwise. I don't go in for the athletes as role models thing (I'll be teaching my son that professional sportsmen are to be admired for their skill and not automatically admired or emulated for anything else ... if you want a role model look to Martin Luthor King or Fred Hallows), but his carry-on casts an unwanted shadow over the game. If a coach bags a referee after the game, he's fined. Same with cricket players. I reckon a penalty on the field (geeze Robinson has no sack ... I reckon he didn't make a report because that just makes his lack of action look even worse "It was unacceptable, but I was too gutless to do anything about it at the time.") and a fine would be appropriate for what Thurston did. Without a fine, though, there's really no deterrent for players to not go off at a ref in the dying seconds of a game.
There's no way the NRL can consistently enforce something like this with suspensions. It's just too murky and subjective, and arguably the punishment wouldn't really fit the crime.