I am the super admin of a site and there are forums I don't have access to.
Admins are not moderators and shouldn't automatically have access to all forums and moderator tools.
Well, my point was merely a technical one, not a policy one. The irony was writ large and had a comedic angle to it for me, so I took a screenshot at the time to show my friends. That particular forum wasn't restricted anyway, I was just expanding the forums a little.
If you're the top admin* ie you own that whole forum / site like I do with nerdzone.uk, then I think access to everything is a right, not a privilege. It's the only staff member who has the rights to everything and not privileges granted by someone higher. All secondary admins have privileges and can't dethrone the super admin.
While moderation is split from administration in XF so one has to enable it explicitely (good, flexible feature in my opinion), an admin is a complete superset of a moderator, hence there's nothing that a mod can do that an admin can't do.
Perhaps there are edge cases where legalities come into it if there are business interests at play and signed contracts say, but then forum software probably isn't the place to put such sensitive information anyway.
Having said all that, there aren't any areas on my forum which are controversial in that way anyway, although I do have private areas, of course.
*I'm using the generic term here rather than super admin as this point isn't specific to XF.