Here's my view on the subject of "rulings over rules."
DM judgement is a potent and a finite resource. Potent: It can easily achieve a level of plausibility and nuance that would require an encyclopedia of rulebooks and an army of rules lawyers to produce through formula. And it can do so without hours digging through books to figure out what rule applies in this situation. Finite: The DM is a very busy person, with only so much time and attention. She's got to create and keep track of countless plot elements, run most of the combatants in each encounter, figure out how NPCs and creatures will respond to PC actions, and keep the fun going. Every time the DM is called upon to adjudicate a rules question, that's a drain on her mental energy from the other business of running the game.
1E and 2E understood the potency of DM judgement, but not its finiteness. They relied far too heavily on the DM to make everything work. 3E and 4E understood the finiteness of DM judgement, but not its potency. They tried to codify everything in rules so that the DM would never have to make judgements at all.
Hard rules ought to cover common, expected situations. DM judgement should be used for oddball corner cases. For example, you could leave it up to the DM to decide the AC value of common armor like leather, mail, and plate. But that's not a productive use of the DM's time, so the AC value of standard armor is codified in the rules. On the other hand, what if a player cobbles together patchwork armor out of sheepskin, metal serving trays, and a cookpot? Writing rules to cover this sort of thing would be absurd. So the DM's judgement rules, using the book AC values as a guideline. Some scenarios, like social interactions, are too complex for hard rules--they're all corner cases. So social interaction is left mostly to DM judgement, with the assistance of a few simple tools like Persuasion checks.
However, there is a difference between limited rules (which codify certain things and leave others to the DM, perhaps with guidelines) and ambiguous rules (rules which clearly intend to codify something, but whose meaning is unclear). The latter are never a good thing. Resolving ambiguity in the rules is a pure waste of the DM's judgement, as well as a recipe for arguments at the table*. A rule should be clear on what it means, or not exist at all.
[SIZE=-2]*And on these forums.[/SIZE]