Sorry for the delay; I had a lot of work to do, but I wanted to comment on this:
Yet the more I learn about the older players and GMs playing OSR games, the more I start to doubt that. One thing that is the most puzzling to me are "classic TSR modules". Except for the GDQ series, none of these seem to have any story seeds. "There is a dungeon and you go there because it's there, and you're adventurers and that's what adventurers do."
That has overwhelmingly been my own experience with D&D throughout the years.
I think you might have put forward another element that makes a game feel like an OSR game with that paragraph. OSR games feel like the fictional world matters and the rules and procedures are about adjudicating the shared fiction rather than being an end in of themselves.
They can absolutely be played that way. I ran a Basic (red-box) D&D game in school that worked out something like this. And I also played D&D with another GM who created a very evocative setting. But in my experience, it isn't typical. And if we restrict ourselves to oldschool D&D, neither the rules nor scenarios supported imaginative play. You're familiar with Dragon Warriors, I think, so I'll ask if you remember
The King Under the Forest or
A Shadow on the Mist - maybe Runequest could set a mood the way Dragon Warriors could, but D&D simply didn't.
I think the disconnect here is that in old school play you don't attempt to "create the story" at all. The fiction I'm talking about is not a story in the literary structure sense. It's the content of the description of the participants. You play to see what happens and what you can do and let any "story" just emerge as it does (more on this below).
For many players, no story emerges beyond that seen in a typical game of chess. The opportunity is there (in chess as in rpgs!), but it's seldom realized.
I think it's worth mentioning that in my study, while I predicted and found a negative correlation between the imaginative or aesthetic personality and liking for D&D, it was primarily the older D&D games that were responsible for this correlation.
Moreover, shouldn't we expect this on the basis that creative neophiles will always be exploring the newest shiny thing, while their less adventurous counterparts are satisfied with the same old routine?
Which might highlight another common element to old school RPGs. Playing to see what happens.
It's a lot of fun; it happened two weeks ago in a game I ran. One of the most memorable scenes was a random encounter with a goblin, who stymied the adventurers with a rolling fog. The little sprite snuck in and stole one of their scramasaxes, dashed away into a copse of trees, and called the wolves down on them. At every turn, the adventurers were just about to catch the little thief, but they were never coordinated enough, or rolled luckily enough, to do it.