If these items are identical, why is there some reluctance to buy top dollar gray products? The warranty is reduced for the gray products but companies like Adorama will give the same guarantee as the manufacturer.
Nikon USA won't work on gray market products even on a fee-for-service basis. They also won't sell certain parts except to Nikon Authorized Repair Stations. Adorama is not so authorized for all Nikon products, so the repair might take longer while they locate parts or send the lens to an authorized firm.
Also, while it isn't a big concern for a company such as Adorama, should the seller of a gray market item go out of business, your warranty will go with it.
Finally, gray market lenses typically sell for less in the secondary market. So should you decide to sell your lens in the future, you may well find that buying a gray market product ended up costing you money instead of saving it.
Should I go with gray products or stick with Nikon USA?
It depends on how you value the risks compared to how much money you save. Personally, I've purchased one gray market lens and a few gray market filters in the past, but I stick with authorized imports for major purchases.
"There is no real magic in photography, just the sloppy intersection of physics and art." — Kirk Tuck