The GTR and the ZR1 both come from automobile companies that make hundreds of thousands of cars - far more than Lamborghini. The GTR and ZR1 both come from companies that have (well... kind of for GM) discovered the profitability of economies of scale and scope (am I losing you?).
Sure - I can certainly understand your point in the case that some dbag buys a lambo just so that he can say he has a lambo only to discover that his headlights are from a Nissan.
My point is that - the guy that bought the lambo because of it's history as one of the worlds finest automobiles, collect ability, performance, lack of annual depreciation and pure love for the world of cars will not care that Lamborghini chose to save that R&D money and invest it into another portion of the car.
90% of Ferrari owners, Lambo owners and other exotic car owners are douche bags - The other 10% are the Jim Fuchs, the Andy Schroeders and other true gentleman that appreciate the car because it's a piece of art and respect the historical significance of those cars.