From Rod Trent's myITforum blog:

Systems Management Server 2003 and 2003 R2 Support Date Extended: Both the Mainstream and Extended Support dates were extended once the follow-on release, System Center Configuration Manager 2007, was released to manufacturers. This announcement is in line with the Lifecycle Policy that states a product will remain in Mainstream Support for two years after the follow-on release. Therefore, Systems Management Server 2003 and Systems Management Server 2003 R2 will transition from Mainstream Support to Extended Support on January 12, 2010.  Extended Support will now end on January 13, 2015.

I wonder what the original date was?