Usually, when we run ls -lwe can see such picture -rwx...- so the owner always has the full stack of permissions.And usually the owner of the system files is the root. Are there any system files where the root doesn't have all permissions, e.g. only read? If they exist, why do they have so strict permission policy even for the root?
System files with strict permissions
permissions;files;root
Files that aren't meant to be executed don't have the x permission even for root so he doesn't accidentally execute something.  Files that root should think twice before overwriting lack the w permission for root. Root can override this without changing the file's permissions, but most programs prompt before doing so. I believe read permission isn't checked at all for root.  