Any restrictions on modern hardware are likely to be strategic. For instance, the reason you can't make voice calls with the ipad and that it doesn't have a camera is most likely because that would mean you no longer need an iphone.

The parts would have added another $5 to the total cost, if that. It also gives them a reason to sell you a new one a year or two down the line. Along with less anemic ram, needed for this amazing new feature called multi-tasking.