@Bas: I know. It's like calling a notebook computer Sony Vaio Windows 8 Pro.
I chalk this up as another example of Microsoft trying to be like Apple with its iPad, iPad 2, New iPad (which has Retina Display), and iPad with Retina Display (not to be confused with the New iPad, which is know old but but also has Retina display).
The only difference is that Microsoft is tying the version of the hardware to the version of the OS rather than some arbitrary name. So when Windows Blue comes out, your old Surface Windows 8 Pro will become Surface Windows 8 Pro with Windows Blue.