The gray market issue has been around for years. Most of the time there is a low likelihood of repair, so the warranty is not a problem. But a 5 year warranty is really quite nice.
Some repair parts are simply not available to third party repair shops - even Nikon Authorized stores. Many times the camera body needs to be sent to Nikon for repair - Nikon Authorized repairs to the main processor may not be possible. I recently had a Nikon CX lens for the V1 require repair - and it had to go to Nikon for service from a Nikon Authorized shop.
Nikon Authorized shops can perform warranty repairs for Nikon USA. It requires the same documentation which they submit to Nikon for reimbursement.
I worry a bit more about complex products needing warranty service. Simple manual lenses or teleconverters have less that can go wrong than today's VR AFS zoom lenses. VR and AF tracking are common repairs. These repairs typically cost $2-300 if not under warranty. That makes it hard to justify repair to inexpensive lenses that are out of warranty.
It's interesting, the issues with gray market extend to used gear. Nikon will not handle gray market gear even if it is used gear not covered by warranty. Nikon Authorized shops will handle gray market gear but there is a chance they cannot get parts or might have to send it to Nikon - where it would be declined if it is gray market.