Just Wondering

Why is it that this very useful app costs $1.99 when purchased for iPad or IPhone, but sets one back $29.99 when bought as Photo Copy as an app for an iMac. I know that, traditionally, app for computers proper are pricier than the same or similar apps for iPad or iPhone, usually about double the cost, sometimes triple. But here it is 15 times more expensive. Will someone explain this disparity to me?

Ms Annie A about PhotoCopier