Hi,
Before going further,we’d better confirm the difference between Computer Configuration and User configuration. Computer Configuration in Group Policy is applied to computers, regardless of who logs on to the computers. User Configuration in Group Policy is applied to users, regardless of which computer they log on to. If we set the settings collide with each other in Computer Configuration and User Configuration in one GPO, the Computer configuration will override the User Configuration. For details, please refer to the following article.
http://www.theeldergeek.com/gp06.htm
Computer Configuration
http://technet.microsoft.com/en-us/library/cc736413(v=ws.10).aspx
User Configuration
http://technet.microsoft.com/en-us/library/cc781953(v=ws.10).as
Based on my experience , the policy 'turn off the notification and action center 'is based on user settings, it can be applied to users only, not computers.
So when you link to the OUs(containing the computers),it will not applied. When you configured it through the default domain policy , it applied to all the domain users .
Best Regards,