From what I can tell, pre/pro's don't sell in nearly the same volume as receivers do. As a result, pre/pro's need to have bigger profit margins factored into their price in order for the companies that sell them to recuperate the investment and make some profit. Those who buy pre/pro's usually are also willing to pay a lot more than the typical person looking for a receiver, so the higher prices for pre/pro's is supported by their niche market.
Also, the components and build quality of pre/pro's is supposedly superior.
I'm currently agonizing over whether to go receiver or pre/pro-amp. Don't know if I'd be able to hear the difference in prices ...
