[Steve Plambeck]

Just my own conceit, but I like to think of dragons (being magical in nature themselves) as born knowing and understanding all the spells, including a few the rest of us have lost, forgotten, or never heard of.

Thus they aren't fooled or surprised by any spell, and understand the limits (costs and duration). But they never cast any, because, well, they're dragons and feel "above all that". It would hurt a dragon's pride too much to ever need to use one.

Someday I'll exploit the plot point inferred by this: a dragon could teach a wizard a spell, perhaps one they couldn't learn from anyone else, but what on earth could a wizard offer a dragon in return? After all, they (usually) don't need anything from us, and what they do want they just take.

I think of demons the same way, knowing all spells but using none. Here of course the RAW speak to the matter, saying demons never use spells, but that doesn't rule out that they could understand everything about them.

And it all amounts to no more than background flavor, but one I find savory.