I don't think it's trivial. The code given to Apple is not modified at any point before sent to a device. The code is also duplicated onto itunes, which is how

I don't think it's trivial. The code given to Apple is not modified at any point before sent to a device. The code is also duplicated onto itunes, which is how you can so easily crack it. The only way I know of to identify each and every purchaser is to use in-app-purchases.