Yep. Let's not forget:
NT 3.5 = kernel version 3.5
NT 4 = kernel version 4
Windows 2000= kernel version 5
Windows XP = Kernel version 5.1 AND kernel version 5.2
Windows Vista = Kernel version 6
Windows 7 = Kernel version 6.1 (WTF OMG so retarded)
Windows 8 = Kernel version 6.2
I know they want to be all pure about their major numbers and whatever, but really they should just get over it. Windows7 is a major release different to Windows Vista, regardless of whether the NT people think it's a pretty minor change.
There's also an app-compat thing going on as well: http://blogs.msdn.com/b/oldnewthing/archive/2004/02/13/72476.aspx but frankly in this case I don't think that's a good enough excuse.