First, let me say this is a great thread.
Second, let me say that I think that it's a false dichotomy. There is no such thing as "old school" or "new school", and that all the people who invented the concepts are really saying is, "It feels me to me like how D&D was ran by my DM back when I was younger than it does like the D&D as it is ran by my DM now." Or even more to the point, "I approach the game more like I approache the game back then, than I approach the game when presented with rules for 3.X"
Or in other words, they really don't understand Celebrim's Second Law of RPGs:
"How you think about a system, how you prepare to play it, and how you approach the game is more important than the system itself."
By altering the system, they are altering for themselves, how they think about the game and how they feel about it. But they aren't actually changing the game. They are changing themselves. They've simply created a system that they (mostly) won't ruin by playing in a way that they don't enjoy and attributing to that the specifics of the system. In my opinion, it's a sort of willful blindness.
I've been playing since like 1981. When I wasn't the DM, I was almost invariably the thief. Now, back in 1984 (let's say), which of the scenarios described in the first Zen of primer (the one about rulings instead of rules) described play around my thief searching for a pit trap? The answer is: neither one. Because even back in 1984 both approaches were supported by play. I could (and did) probe ahead with a 10' pole. And I could (and did) roll against my 'find traps' check to try to determine if my probing with the pole had missed the trap (or vica versa). Moreover, many DMs did require I specify rather exactly what I was looking at when making a 'find traps' roll, so that to a certain extent to do one I had to do the other. This was never an 'either/or' world; it was a 'both/and' world right from the start.
And let's not overlook the willful blindness involved in distinguishing between 'rules' and 'rulings' in the first place. Just because a 'ruling' isn't part of the book, isn't formalized, and isn't written down doesn't mean it isn't a rule. Creating rules on the fly and off the cuff is still creating rules. Common Law is still law. The real difference so far as I can tell between 'rulings' and 'rules' is how the player makiing that distinction approaches the game. He's giving himself permission to play in a less hidebound, less metagamey, less rules lawyerish way by conceding that in this new game it won't be appropriate. But you could make those concessions as part of your approach to the game without changing the system.
This attempt to separate what in my opinion was never separate in the first place is a I think a hallmark of the retro-clones and OSR games. It's not actually recreating games as they actually were, so much as at best recreating games as you wanted them to be or were for you then but not are for you now because you changed or your group changed.
Take the division between Heroic/Superheroic. Again, it wasn't either/or, it was both/and. I had characters that started out as weaklings evolve into the mightiest beings on the planet. That was fully 'old school'. I maintain still that in terms of relative power, the game I played with PC's that were the absolute mightiest in terms of their influence, power, and security was a 1e game. Someone mentioned old school as 'single digit hit points with double digit damage', and yes that is 'old school'. But so was having an 18 con, and being a 10th level fighter or barbarian or cavelier with higher hit points than anything in the game that wasn't a unique extraplanar ruler, moving around in a world where 3d6 damage from a foe was truly extreme and even 16HD monsters (the highest value on the table) needed a natural 16 or better to hit your AC. That was old school too. Old school always supported 'zero to hero' and beyond if you wanted to take it there, and new systems fully support staying in a low level sweet spot if you want to keep them there. I'm 240 hours into my current 3e campaign and the PCs are 6th level. Top that OSR.
Personally I have a hard time going back to OSR style rule sets because I actually remember play as it actually was and I left it not because I didn't like the goals, but becase I remember the problems that highly ambigous and overly situational rules had obtaining those goals. Everyone was always tinkering with the rules back then precisely because the rules were failing so often, and the bodies of Common Law were becoming huge, unwieldy, and cumbersome.
Personally, I don't feel 3e plays all that differently to 1e, except that it is smoother, easier to run, and involves fewer rules arguments.
But that's almost entirely because of the way I think about the game. I fully understand that if you think about it differently, you get different results.