Exchange 2013 - Global Catalog requirements

Does Exchange 2013 require a Windows Server 2008 or later global catalog server? Or is Windows Server 2003 SP2 GC or later will work?

Microsoft says windows server 2003 SP2 or higher will work:

http://technet.microsoft.com/en-us/library/aa996719.aspx

A lot of sites like this one says it requires windows server 2008 or higher for the GC:

http://www.windowsitpro.com/article/exchange-server/exchange-server-2013-143174

Which one is correct?

Also, what is the minimum forest fucntional level and domain functional level?