Hockey is a violent sport to begin with. So say the NHL bans fighting, which would mean the bar for being charged with assault for an on ice punching incident is lowered.
But what about spearing, or knee on knee, or hitting from behind at high speed into the boards. These actions are more dangerous than throwing a punch or two.
It's generally very difficult to separate out game actions from a bonafide intent to injure / maim. Where the intent to injure is quite obvious, players have been and will be charged. The famous incidents involve Bertuzzi, MacSorley, and Ciccarelli, all charged and guilty.