I would just add that my D7100 appears to be fine, and with the 18-140 lens it came with it was always nice and sharp. I've used a number of different lenses on it and most appear to be right on without adjustment. However, the two I've had to adjust were the 50/1.4D, which my wife got years ago for an F100 and which was always disappointing, and the 16-85 DX zoom, which I bought used. I suspect that perhaps that 16-85, aside from not being as crisp as the 18-140, might be a little more problematic in tuning as well. A quick and dirty indoor tune came out with considerable improvement at +5, but it is still a little variable depending on distance and zoom, and never killingly sharp. At some point I'll do a more thorough, outdoor-lit test, but I suspect that comes pretty close. The 50/1.4 has become rather nice with its new calibration, after years of neglect owing to its disappointing softness.
I'm guessing here, but imagine that the very high acuity of the D7100 might make tiny focus errors show up more readily, at least when you pixel peep, and that some lenses, of which the 16-85 might be one, may just never satisfy at all distances and focal lengths. But in this case I'm much more inclined to blame the lens, which visibly back focused on the D3200 as well as on the D7100. Almost every AF lens I've tried on the D7100 has been close enough not to calibrate, and the MF lenses appear to be correctly focused when the dot says they are. Fortunately, it seems a good bit easier to confirm good focus than to fix it when it's bad.
Akira's observation about AFC versus AFS seems interesting, and worth further investigation. On the D3200, I'm pretty sure the opposite applied, as it's noted in the instructions that focus priority in AFC is relaxed and there's an implication, as usual for Nikon never quantified, that the focus itself is a little sloppier. It's very hard to judge, especially as lenses themselves vary, but it seems, looking at the focus confirmation dot, that the area considered "good enough" is a little wider. But if the area is the same, I'd expect AFC to work a little better because it keeps adjusting after the initial hit, rather than stopping as soon as it finds that "good enough" spot.
