D&D has always inhabited a sort of in-between realm, stretched between the classic sword & sorcery fantasy works – which have a very particular take on a lot of aspects of everyday life – and being much more medieval than most really popular fantasy has been. But I think certain aspects of how medieval people thought have been neglected because we let our modern understanding of how the world works shine through too much.
It's the kind of thing I'm reminded of when I find an article like this. Medieval people saw cotton plants, didn't know what it really was, and figured (based on what they did know) that it was a plant that grows sheep. That's unscientific but ten different kinds of awesome for fantasy purposes. Regardless of what you feel about how the real world got here, the fantasy world is explicitly creationist – which was the default assumption of people in the middle ages as well. And, acting based on that assumption, they came up with some pretty interesting theories of how things came to be as they are.
Unfortunately, I think the tension between D&D's pulp S&S roots and the attention to medieval detail got washed away, to a great extent, by settings that internalized big chunks of what I think of as "Tolkienesque" fantasy (the mode of modern high fantasy; the biggest epigone being Terry Brooks). Which is a shame, because I think there's tons of useful material that could be wrenched out of not just the various facts and names of the medieval world, but how people used to think. I've been spending a lot of time lately on considering just how superstitious people really were; they weren't stupid in any way, they just lived in a time where the best explanations for natural phenomena involved unknown forces acting in barely-explicable ways.
There are two ways, both of which I think are quite valid, of approaching magic. One is to assume that the world operates pretty close to how it does in reality, but there's also magic stuff. Some people play up the otherness of such magic really well; it's the intent of all the stuff that was so controversial in Geoffrey's Carcosa, for instance. But I think there's a second way, where the laws of reality really are like people believed them to be. Numbers have deep mystical meanings, which actually has some bearing on outcome. Herbs and stones and gems really do have the properties that people ascribed to them, not because of some weird medical coincidences, but the innate properties of life work like that. I'm talking about going the way that says that what you read in the medieval bestiary – the weird stuff about animals born from plants, or having unconventional internal temperatures, or tearing open their own breasts to birth their young – is true.
It's a vision of fantasy that I think deserves some exploration, and I really think that incorporating it could bring a very different feel than most modern high fantasy, rooted in history and painting the world several shades of fantastic. I think it's where I want to go with the work I need to get back into on my OD&D miscellany.