well if they were to put in a customer loyalty program (call it blizzard bucks), it would be designed to try to get people to spend MORE overall in the game than they do now, both in context of keeping subs active longer AND getting players to spend more on services than they do.
Maybe give a blizzard buck for each real dollar spent (work out a way to deal with gbp/eur/dkk/etc., that would be simple compared), then let *selected* store items be purchased for a blizzard buck price 10x or so their USD$ price? Need a way to allow partial payment with blizzardbucks rather than dollars to hook people in (people see a 50 blizzard buck balance and want to use it, and end up using their bucks and spending more anyway). Maybe restrict bucks from being used for game-impacting things like xfers, racechanges, instant90s, etc.
They have sharp marketing folks, I guess they would know if such a plan would actually generate greater net revenue for the company. It isn't immediately clear that it would, or at least notably, just brainstorming it.