Let's say a player finds out who their future opponents in the tournament are and sends them the following message on ICQ: "Hi, we're playing in the tournament (tournament name), let me know exactly when you can play."
It's a single, short, and somewhat formal sentence. The opponent is simply obligated to provide a detailed response about when they can play; if they remain silent, they have de facto acknowledged that they will receive zero points for not showing up to the game.
However, if I write to my tournament opponent - "Hi, want to play a game?".
He agrees and loses - but I won't be able to prove that we played in the tournament: the person will logically argue that it was just a casual practice game, and there was no mention of the tournament in my invitation; he was also just playing a casual game.
In general, formality hasn't been canceled; a couple of normal phrases to the opponent with an invitation to play - and there's no need to create multi-page threads later about who was a jerk, IMHO.
And why are people now waving their fists after the fight - the tournament is officially over. And the judges need to think about how to prevent this from happening again in the future, as well as the players.