In terms of a database or a system, it is very easy to keep track of a person's purchases around the world. I think why Hermes is not doing it is because of implications regarding privacy, country laws, etc. They are trying to avoid lawsuits that would arise from keeping your credit cards. personal info, etc, in file and connected across the world.
I once got a giftcard out of the blue from LV for a settlement for a lawsuit that had something to do with them keeping credit card infos. I was in no way involved in that lawsuit but I guess it was a blanket lawsuit that they settled everyone who had purchases from a particular timeframe.