The point is well taken that the legality of driving the car on public U.S. roads may affect the warranty in some way. But the more general counterpoint is that, as I said, it would seem pragmatically wise from Merc's perspective to fix their 1.7 million dollar car, given their competition in this niche market. Maybe the dealer/owner would write a contract for the buyer specifying that the car would only be driven in certain legal circumstances for warranty purposes...I don't know, but that seems beside the point to me.
And this is hardly a bone of contention with me personally: there are many more important things I could do with that much money than buy a car. The situation just struck me as rather bizarre.