Basically it's how every game should be. FIFA was probably one the first to do it (kind of) properly. Ultimate team, play matches win coins, buy packs.. Or spend money, get points, buy packs. It's all the same. Alternatively, create content that will actually keep people happy and busy (vast amount of content that's different and unique from the rest) and people will probably be happy to keep paying full amount for it. Rather than releasing it section by section, like pages from a book.