Not sure about this. Windows Enterprise was never sent the nagware bits. I use Win8.0 Enterprise at home (MSDN) and it's never asked me once. I tried to manually upgrade to 10 and it refused. One PC has never been domain joined.
So it might be the fact that it's the Enterprise version of the OS, not the domain join.
So it might be the fact that it's the Enterprise version of the OS, not the domain join.