While reading a post by Erik Person about iOS and Android’s exploit prices, he used supply and demand theories to explain the price discrepancy. Of note, he states that the demand of the exploits are the same, so it implies that higher cost of the iOS exploits is due to the limited supply of the iOS exploits.
However, I’ll add that there may be a demand effect here as well. A recent study shows that iOS users spend about 2.5 times more on in app purchases. I think we can extrapolate this out to say that iOS users spend more on apps and in app purchases because they are generally the more affluent customers. Anecdotally, I also see many working professionals with an iOS device, thus presumably increasing the demand of such an exploit.
To conclude, while I agree with Person about the differences in supply affecting the price, I also think that there is a demand effect present as well.