Such coupons could in theory be usable anywhere even they could just be single use codes and only mailed to addresses in a given country.

Also blocking would be not allowing someone to buy from your store or not use their purchase in a portable fashion not giving different users a different individualized price break.

Example many retailers send out individualized coupons to customers already, presumably some customers who appear more likely to respond to such coupons by spending more are more likely to be given coupons.

Sure but residents in the poorer country can still exploit this by purchasing games on behalf of residents in the richer country, for a fee. Not everyone games so it's not like they're losing out on anything.