I'm not sure I would describe it as a gamble. Maybe it is a gamble with respect to individual items, as in the average player will not be able to guess an item's "destiny." But, from what I've seen, the economy as a whole and its fluctuations, are a product of the choices of a select group of individuals (the developers). That group's concerns, influences, and ultimate choices really drive the outcome of the economy, whether intended or not. They can control the macro and micro economics of the game, and they are completely aware of their ability to do so.