>Number 1 is most interesting to me. Why do a good number of >people say you need a tripod with D800 to get maximum results? >Yet the same is not said about the D7000?
You weren't a member here when the D7000 was released, so you may not be aware that we saw at least as many posts then from new owners who were disappointed with initial results, and extrapolated their own experience to suggest that the D7000 had inherent design flaws. Whilst a few people did indeed have faulty cameras, the vast majority of those with complaints found that things improved once they better understood the camera and how to configure and use it. And it wasn't just the D7000 - it has been a recurring theme over the years when new models were introduced and folks migrated from a more forgiving camera.
To come back to the current situation, numbers 2 and/or 3 of your possible causes are the most likely. The majority of responses in this thread alone show number 1 to be untrue. Even allowing for the fact that a number of D800's have suffered from a left-side AF problem which Nikon have been sadly slow to fix, it is clear that not all of them been faulty. The fact that you still offer it as a possibility might lead a neutral observer to wonder about your motives