After just upgrading my server on my home test network from 2008 RC1 to RTM I noticed something strange showing up in the system properties. The machine was showing up as “Windows Server Version 6.0 Build 6001: Service Pack 1” . Having checked winver from the command line it also thinks that the machine is running service pack 1?! How strange. It must be something wacky happening as part of the in place upgrade from the Release candidate build. Everything else on the server seems to be functioning perfectly.
The images were taken with print screen and edited in mspaint just to blank out my information. The image was from a remote desktop connection to my server.
Incidentally the upgrade path on my single domain was from 2003 ent -> 2008 RC1 -> 2008 RTM and both upgrades happened seamlessly preserving both my settings and all my Active Directory.
It looks like its on purpose to bring the code base to the same version as Vista. This means that vista and 2k8 can share the same patches etc… (see here for more info)