The menu system is tied in with the content access control system: if users don't have access to certain pages, they will not see menu items that link to those pages.
If none of the menu links in a certain menu are accessible to users, they won't see that menu at all.
Example:
- Administrators can see the full Administration menu
- Depending on their permissions, content editors usually see a partial Administration menu
- Anonymous visitors don't see the Administration menu at all