Sorry to dredge up an old thread, but I thought it was an interesting topic.
Less than 300 F40s were made for the US, and only 50-something F50s were sent here. Combine those low numbers with an increase in value, and people seldom unVelcro the diaper. Lastly, for most people, these are not easy or enjoyable cars to drive. Today's standards were yesterday's luxuries, and so the power everything seen in base model whatevers casts an unfavorable and archaic shadow on exotic sports cars whose seating positions are slung unusually low, are equipped with punchline A/Cs, and have manual everything from transmissions to windows. By comparison, the Enzo is a synch to drive, whether you're going to the grocery store, or sitting in 405 traffic.
I need an Aventador!