I can't wait to try this game out. I think this is a cool way to keep people playing, which is actually I'd argue good for the consumer too, because as long as there are people interested in playing it, there will be less times waiting in lobbies for games to fill up. I hate how in old Xbox games it takes forever to find people to play with. If it doesn't have Call of Duty or Halo attached to it, you can wait like 5 minutes just to start a game that will last 2 minutes.
I wonder if it has to be 43 million kills on each network (i.e. 43 million on PSN, 43 million on XBL). If it's counting kills for both, it shouldn't take that long to unlock that fourth map.