Microsoft kinda gave up on this ruse back at Longhorn and Vista SP1 days. Longhorn was a fork of the Server 2003 codebase, and Vista SP1 was a backport/newfork

Microsoft kinda gave up on this ruse back at Longhorn and Vista SP1 days. Longhorn was a fork of the Server 2003 codebase, and Vista SP1 was a backport/newfork of changes made to Server 2008. (Server2008 and VistaSP1 were both released Feb.4.08.) They were absolutely released in lockstep. Vista SP2 was released April.28.09 and Server 2008 R2 was released Oct.22.09. At that point the consumer product became the testing ground for the server kernel. It's easier to think of Vista RTM as a giant public alpha, and and Vista SP2 as an insider preview for Server2008 R2 / Windows 7.