@B G Kavinga is correct. You are explicitly disallowing access to the default scope for those users. If they are editing something that can be done at the website or store-level as well as the default and the "Use Default" checkbox is selected, they would see the default value for the next level up.
In the case they have website-level access they would see
In the case they have store-level access, they would see
The store-level would never be able to see the default-scope value, unless it happened to be the same as the website-level.
You may want to consider giving your admins website-level access, which would give them the ability to see the default-scope values, but still be unable to edit it beyond the website-scope.