Let me try explaining this from the top.
Each permission is associated with two groups: an interface group and a permission group. Interface groups determine which header the permission appears under in the control panel, and have no functional consequence. Permission groups, on the other hand, can change how a permission works.
Currently, the moderation permission is in the "general" permission group. Permissions in this group can't be changed on a per-node basis. The "forum" group, on the other hand, can be changed both globally and per-node. If the permission were moved to this permission group, it would behave exactly like a combination of the currently-implemented option and permission.
As it stands, the option has the functionality of a permission. From a UX standpoint, this is poor design. It's unnecessarily complex and confusing. Users don't understand the relationship between the option and the permission. By eliminating the option, the permission would be much simpler. The title could be changed to something less confusing and it would still be technically accurate, and we wouldn't have to worry about the relationship between a permission and an option.
Functionally, it's exactly the same. However, it's a better design.
