I do photograph landscapes, but I admit that I need a jack of all trades. Michael's point about many tools at hand is right - I have a more limited option set. The D800 and Mk III cross DR performance at around ISO 800 (http://cdn1.mos.techradar.futurecdn.net//art/cameras/LabCharts/Nikon/Nikon_D800_TIFF_DR-580-100.JPG
) which is not to say that the D800 is bad above D800 in my experience, but the DR advantage that I saw with the D800 (especially pulling from darks) was most useful in the lower range and it wasn't so compelling that it kept me from moving to the 5DMk III because of the focus.
I'm often out with my camera on an AS head and Gitzo set of legs an a cable release, but I'm also shooting at the higher ISOs now because they are so clean. I'm not down on the D800 as capable of wonderful images - I made some nice landscapes with it (https://www.facebook.com/media/set/?set=a.524050787620648.139510.182213301804400&type=1
) But I do find its AF and higher ISO performance in the Mk III really useful. I agree those issues vary by user, although I found the D800 focus to be frustrating, even in my landscape work if I was shooting with the lens more open or wildlife (part of that was AF, part of that was the Nikon's LCD zoom implementation - it's much easier to MF zooming in on the screen with the 5D Mk III, but that may also be a lack of better MF know how on my part).