I don't relish the idea of adding fuel to the flame-war, but I might as well put in my two cents.
I consider myself a part of this so-called "old-school renaissance," although I'm rather an aberrant element within it. I don't care for Moorcock and Leiber novels; I don't believe that "real D&D" ought to be plot-free swords and sorcery; I despise the "sandbox" campaign style; and when I run OD&D, I use a friggin' skill system, because I don't have time for my players to pat along the dungeon walls with 10' poles until they find my "DM fiat."
(What's more, I think people are right in saying that "old school" makes the whole movement sound exclusionary. I prefer "retro" myself. The Retro Renaissance... yeah, that's the ticket.)
But what's really at issue here is not whether nostaliga or emotion are playing a part. Obviously they are. Duh. What matters, and this was the essence of the Grognardia post, is that older RPGs have objectively different qualties from newer RPGs. This should not be a controversial statement, but apparently it is.
Think about it. Different RPGs with different rules have real, actual differences that make certain playstyles conducive. You could certainly try to run a hack-and-slash dungeon crawl with the Vampire system or the old Cthulhu system, but who the hell would ever want to? They're not meant for that! Vampire is for storytelling! Cthulhu is for maddening horror! You turn to D&D for dungeon crawling!
Ditto for different editions within a single RPG lineage. Presumably, different editions of the game have different rules. (Or so I've heard, anyway.) It only stands to reason, then, that the rules themselves (and the descriptive text that accompanies the rules) will lend themselves better to whatever play style is popular at the time.
Each edition gets its own zeitgeist. When the 2nd edition AD&D books proudly proclaim, "this is not a combat game!", you take it for what it is and run a plot-heavy, setting-rich 2nd edition game. It will have a different feel from a 1st edition game or a 3rd edition game or an Original/Classic game.
I happen to prefer Original/Classic and 2nd edition to the other versions of the (A)D&D game because these editions have real, objective qualities which are inherent in the rules and the presentation of the rulebooks, which influence the way DMs and players approach the game, and which make the game more fun for myself and my group.
Are we nostalgic about these editions? Some of us are. Some of us played these editions first, learned these play-styles first, and so, quite naturally, we prefer rules that lend themselves to our favorite play-styles. If I had been raised on d20 v3.5, I would probably feel nostalgia for the play-style promoted by d20 v3.5; but don't tell me that I can easily play 1st edition and "approach it with a v3.5 mindset."
Think about how nonsensical this appears on the surface. "First edition rules; third edition feel!" Maybe it could be done. In theory. But, once again, who the hell would ever want to?