I've mentioned my dislike for the logic that belies the 3.x and 4e rules repeatedly here, but I've never really addressed the heart of the matter. Now, there are people who will tell me that I'm wrong because it is the job of the DM to make the game function and, regardless of what WotC publishes, a good DM will make it work. I take umbrage at that, since the books that WotC release not only train the new generations of DMs, they also train the new generation of players to expect the types of treatment that WotC prefers for their games. Specifically, the underlying presumption that I've grown to truly dislike is that the campaign world is a clockwork mechanism where things react within narrow realms of predictability.
Now, this has its roots in the battle between Enlightenment Theism and Democritian Atomism. On the one hand, we have the belief that the universe is ordered, sensible, and predictable. This is a mechanical view of existence. By the mechanical view, we can predict all things in nature as long as we know enough about the circumstances. At its most reductionist, this is a completely fatalistic system. Determine the exact mechanical starting point of the universe and one can then extrapolate every piece of history that will follow.
In a roleplaying game, player choice will always remain free (even if there are false options—ie, lose conditions that are built into the system). There will also be residual effects of randomness: the range of a sword-stroke's damage, etc. However, these are minute qualities that can be predicted within a certain range. This mathematical purity is even more clear in 4th Edition than in 3rd: namely, you can predict to a very high degree the amount of damage something will be able to do based on its level. There are, in fact, equations to tell the DM the proper amount of damage a creature should be able to deal based on its role, the type of damaging power, and the level of the beast. HIGHLY predictable.
The atomic view posits a different reality. Democritus posited a universe in which small elements bang together rapidly and create confusion for no real reason. Predictability was possible but never guaranteed. The events of the universe were seen as random, thoughtless, and without theme. I believe this more nearly approximates the way the game was played before 3rd Edition came into vogue. It had a heavy emphasis on tables and the random element in NPC reactions (though again, never be fooled into thinking that these were always meant to be random; they were bound to DM fiat and only used if the DM did not know already know these things). Instead of a formula of how much damage things should deal to be challenging, damage generation was generally determined by thinking about how much damage they should be able to deal regardless of how challenging that would be.
But this is all tertiary to the lack of respect for the DM that exists under the mechanical setting. For, in a mechanical view, since all things are predictable a certain set of rules for how the universe behaves (specifically, the rules that affect characters, magic, hp, all of these things) can be written and, once they have been discovered by the players, become the whole of the law. The DM running a game under this rubric is less like a god and more like a true referee. He must judge the manner in which the ironbound laws interact with one another; do they intersect properly? Here it is noted that the way in which 3.x is generally played (or the way in which I have seen it played) does not define "properly" as "a way which tends to mirror reality" but rather "a way which is correct by the books."
Let us take the example of a fall from a great height. You are soaring away on your magic carpet high above the ocean. You are clad in plate armor, a towering golden god of might, when the carpet's enchantment suddenly wears off. Perhaps a rival mage is below onboard a ship, spots you, and disenchants it from a distance. Either way, you are now falling from three hundred feet, tumbling ass over elbow into the sea. The AD&D DM would smile sadly and shake his head, describe the brutal impact with the water and the tidal pull of your armor as your already-mangled corpse descended to the bottom. In this case, he did not make reference to any rule, he simply decided that you would not survive using his own judgement.* The 3e DM would be rolling dice for falling damage and checking to see if the character survived and if, by some miracle of the rules, the character was meant to still be alive, the DM would shrug and say "I guess you made it." At least, that's the way the book is written.
Steve Winter, the guru who's word I usually agree with, has an article about untidiness being good for drama. I would argue that not only is it good for drama, it is a good way to represent the uncertainty of life. You can learn all the rules to AD&D forwards and backwards and still be surprised by an ambush, murdered by bad roles, or killed by falling from a great height. Knowing the rules is no guarantee of survival. Only native intelligence, foresight, and planning can keep you alive. That rankles some people, and I understand why. I just don't agree with them.
*The DM is encouraged to use his own judgement by this very section of the 2e DMG:
There are occasions when death is unavoidable, no matter how many hit points a character has.
A character could be locked in a room with no exits, with a 50-ton ceiling descending to crush him. He could be trapped in an escape-proof box filled with acid. These examples are extreme (and extremely grisly), but they could happen in a fantasy world.
As a general guideline, inescapable deaths should be avoided--characters always should have some chance to escape a hopeless situation, preferably by using common sense and intelligence. This maintains the interest of the players and helps them retain their trust in the DM.
However, if a situation of inescapable death occurs, the character dies, and there is no need to play such a situation out round-by-round. Allow the player to attempt reasonable (and perhaps even truly heroic) methods of escape. If these fail, simply inform the player of the demise of his character. The doomed character is assumed to have lost all hit points.