If a person signed into or su'ed to the root account could not reset a password (either to the same thing or something new) then you would have accounts that would get locked/forgotten-password that you would have to delete and recreate.
Champion,
As far as setting the same password - are you using NIS or NIS+?
The SA has unrestricted rights to the passwd command. And can operate freely unless the SA puts said restrictions on the root account itself.
The SA should be able to set the password for any user, even to the exact same passwd as before.
If as a user you type $passwd <enter>, you are subject to whatever the user restrictions are as setup by the SA, as opposed to the SA issuing # passwd champion. The SA could even set a passwd for a user that violates rules that the user lvls would be FORCED to use if they set their own passwd.