The Fair Price Package was introduced when GoG stopped using US dollars as the currency in every region and started converting the prices into their respective currencies. Since GoG does not update their prices everytime the exchange rates between dollar and GBP or Euro change, they give you a store credit roughly equal to what you pay in excess of the exchange rates. With the exchange rates falling the regional pricing of games gets closer to the dollar pricing in terms of worth and thus the store credit is lowered.