What does that mean "playing by the rules set"? Not flubbing a die throw? Not playing an NPC enemy to his fullest? Throwing 4 baddies at the players when the "ref" originally decided to send in 6?
Actually, it's "rules set out
in that agreement". Here is what it means:
Potential DM: I want you to be a player in my game.
Potential Player: Only if you promise to always roll in the open and not fudge any die rolls.
Potential DM: O.k.
If, during the game, the DM rolls a die in secret and fudges the roll, then he is not playing by the rules he agreed to verbally (well, assuming this didn't happen via email, text message, etc...).
But you seem to already have an answer for that.
Maybe you agree to roll in the open and not flub die rolls or modifiers. Fine. But, there's so many other areas where the GM, ref, DM, whatever you want to call him, can effect the game that, if the GM wanted to play "GM vs. the Players", the GM would win, every doggone time.
Therefore, the ref cannot cheat.
Your argument, if I understand it, is that it's pointless to make a GM promise not to fudge rolls since a GM could simply find some other way to achieve what they want.
I agree that a GM can achieve anything they want via methods other than fudging die rolls, but I think that's the point of such agreements. If the GM makes an encounter harder or easier by adding or removing monsters, then players may feel that's more fair than if they make it easier or more difficult by fudging die rolls.
It's not the end result such agreements are about, their about the method used to obtain the result.
No, it's in every game, even one where there is a referee rather than a GM. Why? The ref makes the calls on what's legal and not legal.
Well, their are limits. For one thing, if the group (players + GM) agrees to play Shadowrun and the GM starts running Paranoia (I'd love to see what happens when the players catch on...) then the GM has broken the agreement. Sure, technically the GM can establish rules, but a wholesale switching of games without player input, could be a breech.
Whether you acknowledge it or not, it's just plain impossible for the GM to "cheat" becuase of the type of job the GM does for the game.
Just remember that if the GM goes to far with this, he or she may not have any players.