A few days ago I broke my silence on the Wizards of the Coast website concerning D&DNext. The question posed by the developers was one concerning the new feats in 5e and namely whether or not they should have roleplaying effects, combat effects, or exploration effects or all three. I was irritated at the very way the question is posed, and I posted a response that suggested that new abilities should make sense in totality; if someone can breathe fire, it makes sense to allow a ruling that says their fire breath also sets things on fire, boils water, etc.
I received a lot of positive responses... but amongst those, I was soundly schooled by a nameless lizard-avatared woman about why rulings were bad. She put forward the argument that rules should be ironclad and stay the same from table to table. The game system must be our baseline, and only from there, with a complete and comprehensive all-encompassing ruleset mapped out should individual tables modify them. I couldn't disagree more.
Gygax firmly believed this as well; every table and by extension every group is sacred. I was scolded and told that rulings were essentially "rules that no one writes down" which complicates and obfuscates the game. But rulings are what make the GM's role essential in a roleplaying game. Likewise, the choices that your GM comes up with at your table are what make it your table and not some other gaming group. By constructing a formal homogeneity that must be obeyed (or altered with careful forethought), the individuality of each gaming group is infringed upon. While government and law should be universal, D&D should differentiate.
What exactly is at stake? In a rulings-heavy system like AD&D, there are a number of things being contested. The most important is the ability to modify the game to the needs of your table. The more complex and specific a ruleset becomes, the harder it is to change any of those rules without breaking others. Making new races or kits (or classes, since kits don't exist anymore) in 3.x or 4e is a tough process. You might unbalance the careful seesaw of the rules, sending the game plunging in one direction or another. In the case of 4e, you also need to understand the bizarre mathematical notation used to determine how much damage powers do at what levels.
This is a severe hindrance to developing new monsters (which is an extremely important element, especially in 4e where every which way a monster may choose to fight must be represented with a special "build") as well as homebrewed settings and material. It makes everything more difficult and time consuming and actually seems to warn that the game is already good the way it is, so why would you go touching it with your grubby GM fingers to alter it?
Second, the feel of your particular iteration of D&D relies heavily on your GM up through all of the TSR editions. If your GM wants a silly game, you will have it; if he wants a serious game, that too can be done. Do you want to do something to make the game more gritty? Optional rules supporting that probably exist, and if they don't you just have to rule in favor of grittier and more realistic outcomes as a consistent element of your playstyle. The same cannot be said in a system that is universally competent.
Thirdly, a system which covers all possible contingencies cannot possibly be easy to use. The fact that a separate rule exists for every situation already means that those rules must be looked up. A system which purports to take all variations into account is either incomplete, lying, or incredibly clunky. The fact of the matter remains that existence is extremely complicated, and representing all of its facets is something beyond even the greatest of systems. Attempting to do so will only result in sorrow, whereas attempting to represent a reasonable number of scenarios and leave the GM to interpret how those rules extend to the rest actually manages to cover everything that could ever possibly happen.
Truly, I feel as though the diversity of games that are being run relies strongly on the ability of the GM to manipulate the so-called core rules to their own desires. The more codified and entrenched these rules are, the more difficult it becomes to do that. I value diversity, and Gygax did as well. Having a homogenous ruleset that is universal, all-encompassing, and complete is neither a viable goal nor a desirable one.