It's not so much to keep the cars exclusive--the limited production numbers do that. It's to prevent speculators from buying up the cars, not driving them, hoarding them away in air conditioned garages under bubble wrap, and then selling them to legitimate collectors and enthusiasts at ridiculously high prices.

This is exactly what happened with the 288 GTO and later the F40. Each car within a few years of its introduction was selling at 3-5 times its original retail price, because speculators bought em up real quick andn then later gouged the enthusiasts.

So Ferrari starting with the F50 started qualifying buyers for it's top-line "milestone" vehicles. For example to get an F50 you couldn't buy it, you had to lease it. And the only way you could lease it was if you owned several other Ferraris, including an F40 (and I think, a 288 GTO, not sure on this one). That way the speculators who never really own a lot of cars at any one particular point in time were prevented from buying up the F50 and it went directly into the hands of legitimate enthusiasts and collectors.

The policy continued with the Enzo--you needed to have an F40 and F50 plus a bunch of other Ferraris to get on the list for an Enzo. That's why you see lots of pictures of Enzos being shown by their owners right next to their F40 and F50.