This is a 5DIII ISO 12800 shot: http://www.flickr.com/photos/davebass5/8040289680/

It looks great to me. Now, unless I am missing something obvious, this could be taken at a twice as fast shutter speed than one could ever do with a D800 (at 6400). That's a feature, and a competitive advantage, that one may find desirable. Certainly the D800 will allow for other things that the 5DIII won't.

Now I, as a novice, amateur, and one who likes to carry his camera around when travelling and "size the moment", I think the ability to use a faster shutter speed is more valuable than pushing the resolution to 36Mpx. Indeed, others will prefer otherwise.