If your social game is not on iOS you won't lose out on that 50% of the market, you lose period. Even single player apps that need to go viral must be on iOS, because network effects are intrinsically social.

It doesn't matter whether your product is Facebook, Whatsapp, Trello, Angry Birds, or Uber. If you're not on iOS you're done. Game over.

If that isn't monopoly power, I don't know what is.