I remember reading somewhere that African elephants use infrasound, which carries long distances in open areas, but that's below the range of human hearing, so we wouldn't "hear" it in the game. I don't remember whether or not Asian elephants do this as well.
I've also read that Asian elephants make more soft chirping and squeaking sounds that African elephants don't, which makes sense in a forested setting where sound doesn't carry as far, so they maybe stand closer to one another and "speak" in more conversational tones? Species living in more closed-in habitats tend to use high pitched sounds to communicate more.
If you're out in the open like an African savanna elephant, maybe it's more profitable to "shout" to your comrades. So perhaps in the game, the louder, deeper vocalizations of African bush elephants are more noticeable to players. But this doesn't mean that Asian elephants don't vocalize just as much among themselves.
I don't know how African forest elephants compare. They are really rare in zoos.