That's what I have noticed. What's worse is that the automatic system only picks up words said during the game, and not before the game (champion selection) and after the game.
For example: in a recent game where both sides were being so salty, I said a few choice words during the game and got their warning of "obscene language" yet, my language was only ONE word in the entire game, where as the other team and the top laner was making a sailor blush with how many words he was using. I reported him, but I doubt anything will come to it.
In a different game, I finally unloaded on someone after the game was over and no warnings ever popped up on my screen. So, the difference between getting one of those warnings that NOTHING WILL COME OF, because I only really let people have it when they tick me off during the game or make the game completely un fun due to script hacks, or abusing game breaking bugs that riot has not fixed yet, is the fact that the words were mentioned while the game was going on and the opponent got mad and did a revenge report.
What needs to change is the automatic system itself, or a way on your character profile to see who gave you the warning and what words were said that lead to the warning. I did hear that they were testing out an automatic feedback system on the PBE, but problem with that is that to get on the pbe you have to not be an excessive negative person (I'm one of the neutral players as i do have my bad days and good days) so the system will be flawed when it hits the live servers because it hasn't gone through the proper testings of legitimate reports.
Again, my suggestion to tweak this system is to give incentives. Back when I started playing in october, they did a "free skin" gift to those that were good in december. (I got a crappy garen skin) They need to do something like that more, or find some way to reward those positive players and give some incentive to us neutral players to be more positive, while giving the negative players a reason to want to change their behavior. As it stands now, Riot as a company is losing out on millions of dollars because they are letting the negative players affect the main area of the game where most of the player base is (Bronze-Gold Ranked and normal ques).
