Right before WWDC, there were rumors of iMessage becoming open to other platforms such as Android, but where is that now? If that's not happening, and if Apple is making such a big deal out of iMessage as they are doing now, I'd say they're just being arrogant or ignorant or intentionally incompetent. No matter how good iMessage becomes, it will simply not pick up unless it's accessible to all major platforms, except in Apple campus.
I can only guess at why they backtracked on their initial imessage plan to make it available on all platforms along with FaceTime, but I wonder if now if doing so would open the service to security risks. After going to supreme court against the gov to protect security, I'll bet they can't just turn around and say they're opening up the service.