I'm still mystified as to why the Authenticate User Solution Recipe shows you how to create an update user page, accessible to admin only, when admin is unable to access the records of anyone except themselves!
The reason is it actually uses two separate pages. The user profile page that the user views and updates is a separate page than the one the admin would use. Both of them pull the same data from the same database table. But the user page uses the database information according to who is actually logged in. But as an admin, since the admin is the one logged in, there needs to be a different way to call up a particular user out of the database.
Additionally, on the admin update page, you may want to be able to modify information that you don't want the users themselves to change, so these type of things can be part of the admin page.