SQL & PL/SQL

Hi,

in the urman 10g plsql book (Oracle Database 10g PL/SQL Programming) for each chapter there is a script to create the user for the examples of the chapter.
Essentially the user is created, permissions are granted, connection is changed to the new user and then tables are created and filled.
When I run these scripts as SYS as SYSDBA they are working.
When I run them as SYSTEM I get an error ORA-01301 insufficient priviledges, when the tables should be created.
So my question is:
Why is it necessary to have SYSDBA priviledges for running these create user scripts?

From the Oracle Documentation I had the information SYSDBA is for creating/starting up/shutting down the database.

Thanks,

Peter