I still don't understand the need for this. We already have this as the iPhone 4 and 4S, and soon the iPhone 5 will be in this category once the 5S is released. Why waste resources designing an entirely new product when they already have older iPhones they sell for less with no additional costs to build.
Despite the factors you cite, Apple thinks that they will increase their total profits by adding this device to their lineup.
From everything I have seen, Apple knows very, very well how to move cash out of consumer's pockets and into the pockets of the Hedge Funds.
Personally, I'd bet that Apple is right and that you are mistaken.