My theory on WhatsApp is that the U.S. is that the iPhone is more popular here than anywhere else and many of the early adopter types that are needed to help a

My theory on WhatsApp is that the U.S. is that the iPhone is more popular here than anywhere else and many of the early adopter types that are needed to help a social network gain momentum use iPhones and have friends who mostly use iPhones, so iMessage is what is naturally used.