Windows 8 comes with Windows Defender. Microsoft Security Essentials does not work on Windows 8, but its features have been integrated with the new Windows Defender.
From Windows Defender on Wikipedia:
In Windows 8, functionality has increased to offer antivirus
protection as well. Windows Defender in Windows 8 resembles Microsoft
Security Essentials and uses the same virus definitions.
System Center 2012 Endpoint Protection uses the same virus definitions as Windows Defender, but also offers IT management for businesses.
From the System Center 2012 Endpoint Protection website:
System Center 2012 Endpoint Protection integrates with System Center
2012 Configuration Manager to provide a unified solution that gives
you a comprehensive security and management solution for clients in
your enterprise. Endpoint Protection uses the monitoring and
deployment capabilities of Configuration Manager to streamline the
deployment of antimalware definitions and uses Configuration Manager
to provide an in-console monitoring solution. You can also use System
Center 2012 Endpoint Protection to configure Windows Firewall settings
on computers in your enterprise.
Because Windows 8 now bundles Windows Defender, you can have as many PCs in a company running it as you like (the 10 PC limit was strictly for Security Essentials). If your IT department would like greater control and reporting over the security infrastructure in your company, only then should they consider System Center 2012 Endpoint Protection.