Well if by 'DD' you mean 'Dungeons and Dragons', and not some fantasy about large bra sizes, then I'd assume that the system's massive array of shielding, absorption and anti-magic spells play a role. From what I recall, the player skills and spells aren't supposed to be an exhaustive listing of all physical and magical activities, but just those that are of use to small-group adventurers (hence the ones that your characters might feasibly learn, while living as adventurers).
Remember, 'adventurer' is basically a kind of job in D&D. Other NPCs might have reason to engage in sculpting, craftsmanship etc that is simply beyond the reach of someone who is living their life on the road. It's why your all-powerful high-level adventurers don't usually have more than a small-to-moderate set of personal lands and don't have armies doing their adventuring for them - a similarly powerful character who was a property developer, or a general, might have that stuff, but as an adventurer you get the skills that form the various adventuring classes.
SO, just as the setting includes stuff like warships, trebuchet and engineering (for plumbing, building, etc), even though your characters won't directly be accessing that stuff, we can assume that it also includes anti-magic building materials, castle walls that absorb destructive spells, materials with resistance, also perhaps buffed by on-site casters, depending on how wealthy the castle-owner is.
Edit:
What I fucking hate is parts in computer games where it tells your max-skilled thief 'sorry, you need a key to open this lock'. These days there often isn't even an explanation, and even in the older days they'd just put something like 'there's a special enchantment', or 'the lock can't be picked'. Surely the ability to pick difficult locks - i.e. ones with magical components and good design - is exactly what my character is learning when I max his picklock skills out! How can he be even a decent thief, let alone a top one, if he can only pick the crap locks? And surely, if this is a setting where magic locks exist, even if they aren't common, the very thing that separates my maxed out picklocker from your junior d-grade tramp is that my guy has the mastery to crack the best systems around? In a magic setting, that means familiarity with magic components in locks.