Of course the D800 can give you good photos at F16, and ISO 800, and slower shutter speeds. Probably even better than many other cameras. What I'm talking about is using the D800 to its fullest potential. Within the parameters I mentioned in my initial posting, you're using the D800 to its full potential, getting the best of the best in terms of IQ out of this camera, and this IQ will considerably exceed the IQ achieve by most other comparable cameras. Outside these parameters, the D800 is still a good camera, only its particular advantage over other cameras is reduced. But it will of course still take excellent pictures.
sk66 is not the only one seeing that the D4 retains color and DR better when the ISO gets higher (in low light, where you really need the higher ISO) than the D800. The measurement values in different reviews also show where the optimal range lies. But the D800 will of course still take photos in excellent quality at higher ISO, surpassing most other cameras. And it is true that to get the maximum sharpness on pixel level, you need (an excellent lens and) faster shutter speeds or a tripod. Your D800's images will still look as good as the image from other cameras or even better if you don't achieve the maximum detail sharpness the D800 is capable of, but in order to use the D800's potential to its fullest, indeed you have to pay a little extra attention to sharpness.
Similarly for diffraction - you will only see the effects of moderate diffraction when pixel peeping. Even F22 is possible. And if you want to use a specific DOF, you will of course use F11 or F16 and still get great pictures. After all, the artistic value of an image doesn't come from technical specs. But fact is, the maximum detail sharpness of the D800 is reduced as soon as you go beyond F8. It is not visible until a few F-stops higher (smaller apertures, higher F-numbers), but for those of us who just try to get the max possible technical IQ out of every image, those are parameters we should respect.
Personally, I have set my max ISO to 400 (silly, I know

) and if I need higher ISO, I increase the setting manually. I also noticed that I can get pretty much detail even if the image has been exposed a bit on the dark side (exposure to the left), but of course, I probably lose some detail in terms of DR and color this way, and I still don't know whether it would be better to increase ISO further instead.
Luckily, for the kind of pictures I usually take, the D800 can be used within the perfect parameters, getting me the max technical IQ, and I don't have to worry about it. So for me, the D800 is exactly the right camera. For the pictures I want to take, I can usually use it within its optimal parameter range. And when I can't, it's usually for images where the max technical IQ is not so important for me (family pics, my kids, evenings with friends).
And this is why I posted about those parameters initially - whoever aims for maximum technical IQ, needs to know about these limits and decide whether this camera is the right one for him. If you are more relaxed about obtaining the maxmium technically possible IQ this camera can provide, then the D800 is a great camera for you even far outside these specs.
I often wonder about these discussions whether a camera is better than another. I usually think that many of these discussions are not helpful, because in many cases, there is not a better or a less good camera. There's just one camera that's better for a particular purpose, and another camera that's better for another purpose.
If I were into video, btw, I'd use my wife's camcorder
