R_J_K75
Legend
However, I think a lot of D&D tropes (especially literacy) draw too much from the Renaissance than from the Medieval Period most associate with D&D.
The one thing that might get in the way regarding widespread literacy is whether one sees the printing press as being too high-tech for one's setting, as I do.
I generally play in the Forgotten Realms, and rarely a few other campaign settings. Most of my games as a result have a mix of technology when it comes to comparable real world historical eras. So I never really considered D&D, even when I started playing in the early 80s as strictly medieval, I saw it as a little of everything. You may run into societies of varying technological advancement and knowledge from adventure to adventure. The only exception was Dark Sun, which is its own thing all together.