I very much like Nikon bodies as well, so I really don't speak as a "supporter" of any of the two systems. But that sentence form dpreview.com really doesn't mean much in terms of how the 6D will compare against the D600.
And, I also disagree partly with it. It seems to me that the 6D was designed to be a quite different type of camera than the 5D Mark III. Think of integrated WiFi and GPS, as well as of the smaller body. One may like it or not, but it seems to me dpreview.com is a bit too superficial in that statement.