I would say that both desirability and rarity influence values. Consider the market values of the '55, '56, and '57 Chevys as apposed to the Fords of the same years. These cars have a cult following. If equipped with rare accessories or a particular body style, the value rises astronomically.
The Fords were just as good cars as the Chevys, however.
So, to an old car guy like me, if you want to have a nice old '50's car for a reasonable price, I'll get a Ford.
In bikes, it would be like the difference between an RB-1 and another high end but less "desirable" Japanese made bike.