Apple sells three
iPhone 5 variants. They also make a lot of sacrifices in order to increase the number of LTE bands that it can support. At the moment, almost no two LTE networks in the world are on the same frequency deployments. From a manufacturing standpoint, that means lots of variants at lower and lower volumes, so higher and higher costs.
An unlocked iPhone 5 costs nearly $700. More than double the N4's price.