As regards my Canadian D200: "Nikon Melville was happy to service it" means that the D200 was indeed repaired by Melville.
My understanding is that in each country (or country group), official Nikon retail sellers may form their own sales organization with their own rules. Thus, in the USA, the US official Nikon retail sellers have chosen to have a rule about not servicing gear which has been imported into the US to be sold by an official Nikon retail seller as a gray market item for a lower price than the "official" imports.
I personally think that the US gray market rule is bad policy. The buyer may save some money (more savings than I had realized as per a comment above!), but if the purchased gear breaks then that buyer is up the old creek without the proverbial paddle
-- you pay your money and you take your chances! While I agree that Nikon gear is quite robust, most of my repairs have been due to my own goofs such as in tipping a tripod over into a frog pond. Or the infamous 7 foot gear leap from a fish gate onto a granite ledge below. Had any of those damaged items been gray market, then I would have had to discard them as unrepairable. [Also note that here in the USA, we have a very strict regulation of who can or cannot repair Nikon gear because parts will only be sold by Nikon to official repair shops, and official repair shops must obey the Nikon gray market rule.]
This was all explained to me by Nikon USA when I wrote to them to ask if my Canadian D200 was considered to be a gray market item. It was not because: My Canadian D200 was originally imported into Canada to be sold there by a Canadian Nikon retail seller, was then purchased as a new camera by a Canadian citizen and finally was re-sold by that original Canadian buyer to me in the US. So my import of the D200 was not considered a gray market item. And therefore it could be repaired by US Nikon Melville.
I hope this is considered a factual explanation of the US gray market thing. And everyone can now move on.