With Server 2012 R2 out; I had to make a few updates to my SCCM Collections to take this into account. Quick and Dirty, for Server 2012 R2, WQL Statement:

select 
SMS_R_SYSTEM.ResourceID,
SMS_R_SYSTEM.ResourceType,
SMS_R_SYSTEM.Name,
SMS_R_SYSTEM.SMSUniqueIdentifier,
SMS_R_SYSTEM.ResourceDomainORWorkgroup,
SMS_R_SYSTEM.Client from SMS_R_System   
where    
SMS_R_System.OperatingSystemNameandVersion like "%Server%"   
and 
SMS_R_System.OperatingSystemNameandVersion like "%6.3%"

Whereas the 2012 (non-R2) Variant is:

select 
SMS_R_SYSTEM.ResourceID,
SMS_R_SYSTEM.ResourceType,
SMS_R_SYSTEM.Name,
SMS_R_SYSTEM.SMSUniqueIdentifier,
SMS_R_SYSTEM.ResourceDomainORWorkgroup,
SMS_R_SYSTEM.Client from SMS_R_System   
where    
SMS_R_System.OperatingSystemNameandVersion like "%Server%"   
and 
SMS_R_System.OperatingSystemNameandVersion like "%6.2%"

You can add both into a single collection to create a single Server 2012 Collection. Easy, easy.