shurai said:But notice that your particular example of Power Attack can actually show how the GM has the final power in terms of the effects of character choices. The DM can easily just mark off the bad guy's hit points as if Power Attack hadn't been used, and say nothing.
Ask yourself, if the DM did cheat this way, how would you know? Is it possible a DM has done this to you already without your knowledge? In a way, the DM's ability to conceal this sort of thing is proof that the DM holds that power legitimately -- it's built in to the game and, I believe, even recommended by the DMG.
Right now some of you are thinking this is shenanigans, but it's a question of play style. Some people hate to fudge die rolls and such because they want to let the story develop without "intervention." I'm from the other camp: If the adventure is more fun with the DM cheating a bit, I'm okay with that. It's not like I know anyway, and I can just as easily squint a little bit and not see the DM doing it.
You'd be surprised at what players can discern at a game.
And personally, I do not think any DM absolutely KNOWS that action A will always make the game "more fun" than action B. People do not have that level of foresight, especially when party decisions are generally made by the players, not the DM. Just having 3 extra hit points of damage on the party Rogue could result in a totally different direction being taken by the players and their is no way the DM is going to be able to anticipate this every time.
The most surprising and fun elements of the game usually come out of spontaneity, not planning.
DM's can fudge all they want. If one does it to me and I repeadtedly catch him at it, I will vote for a new DM and new DMing style. From my POV, he is breaking the social contract when he does that, regardless of whether I can detect it or not. There really is no need to railroad a game in this manner and a DM who does so has lost perspective that there is more than one player at that table.