I find this thread tremendously interesting, and I like hearing what other DMs do when situations like the ones noted in this thread occur. I agree with a lot of the posts, and the others I think are absolutely asinine, and would never go over with my group.
Here's a few notes as to what we do:
My major "policy" is that no PC can die due to mistake by the DM. I will retcon that immediately upon noticing it. The limit, though, is if the player has already rolled up a new character and has been integrated into the party, I won't bother... it wouldn't be worth it at that point.
I also expect my players to know the PHB. The more they know, the better. In fact, I wouldn't complain if they were all rules-lawyers for the PHB (only. Yeah yeah, be careful what I wish for...). Every other book, however, is DM's domain only. I have no problems with players who speak out against one of my rulings and has a quote from the PHB. (However, if they open their big mouths, I certainly expect them to have that PHB ready.)
Because of my expectations of the players' knowledge of the PHB, any mistake they make in their disfavor, results in a "too bad for you" statement from me. As I mentioned above, I expect them to know the PHB. Depending on the situation, though, the same may or may not occur with the NPCs/monsters. If, for example, a combat is complicated with many monsters needed to be controlled by the (poor, overworked
) DM, and I forget something that should have happened (usually no more than) a round ago, I'll adjust. (Eg. Oops - the wraith should get 5 hp for draining a level from the PC last round. I'll add it now. Oops, Joe, your PC takes an extra 5 damage - forgot this Strength mod from the last round) My reasons are usually: players only control one PC - if you can't even get that right, you're an idiot. The DM often must control many, many monsters. There's a chance he'll make a small boo-boo every now and then. As long as it doesn't get out-of-hand or slow the game down overly much, then it's fine (but, of course, there's always a limit).
Finally, I consider this a game, first and foremost, so any retconning is done OOC. Joe died by my mistake (monster took a move action and coup de grace in the same round, for example). Well, he's alive now. My mistake - sorry guys. For our group, we consider owning up to a mistake to be better than retconning "in game" (yeah, a wandering cleric just raised you, that's the ticket...).
As to the original message: If you're DMing for friends, I'd tell them to "sit down and shut their pie-holes" when they question obviously non-PHB-related decisions by the DM. Then, I'd ask "why?". Why wouldn't the golem fall down? Why wouldn't the giant sunder the weapon? And listen to what they say. Usually, the player will often find that his/her reasons are completely idiotic, and shut up. Rarely, he/she may actually state a reason that is totally makes sense but nobody even considered. Who knows? This is unusual, though, and the DM normally gets to rolls his/her eyes, and continue on. I, personally, am open to communication with my players - even if it slows down the game a bit. Works for us, but is certainly not for everyone.
If you're not DMing for friends (I feel sorry for you), I'd skip the "pie-hole" part and just jump to asking why...
In the end, it's your players who will ultimately decide whether the rules or flow of the game is more important. As a DM, I defer to them.
