I'm afraid your conclusions are invalid unless you have handled examples of the SAME item made in multiple countries, and in practice there are not many such items in the Nikon line-up.
The 18-200mm VR Nikkor was initially made in Japan, then production was shifted to Thailand. I've handled both versions and there was no detectable difference in quality. We even carried out a survey here about the "zoom creep" issue with this lens, which also showed no significant difference that could be attributed to country of manufacture.
Nikon has chosen to locate manufacturing of many of its "consumer" products outside Japan, but I've seen NO evidence that this has lowered quality. The fact that a D3 is no doubt built rather better than a D7000 has nothing to do with where they are made.