Tyring to get a better understanding of ORACLE admin accounts
Yes, there should be. Even the documentation mentions that:

Administrative User Accounts


  Create at least one additional administrative user and grant to that
  user an appropriate administrative role to use when performing daily
  administrative tasks. Do not use SYS and SYSTEM for these purposes.


But the database can not force you to do this. It is a discipline that some companies follow, while other companies ignore.