Again, as I stated... it's Apple system. It's their choice.That argument could be used for any tech/app on another platform. I’m sure Microsoft would be happy if Nintendo released Mario Kart for Xbox, but that doesn’t mean Microsoft can just do it themselves. Apple can release iMessage for Android if and when they want to. But it’s ultimately their choice.
But these gaming companies is quite different from what's going in the states with iMessage... Heck, I could get Mario Kart on Android or iOS? Does iMessage exist cross-platform?