digger, the reason Orci and Kurtzman put it on the screen was to indicate their intention. They didn't have the cast discuss it pointlessly. Orci said so.
I agree that was probably the writers' intentions; otherwise, you are correct that it would be pointless to be on-screen. However, in my belief, cannon is determined by what is on screen, not what the writers' intentions were.
If intentions defined cannon, then we have to question everything we believe about either Trek universe until we get clarification from every writer.
Also, keep in mind that, with the example of the on-screen discussion regarding an alternate reality, no where is it said that these characters have proof this is an alternite reality, only that they believe it is. If we have to accept the characters theory as fact only because they mentioned it on screen, then any theory ever mentioned in Star Trek would have to be accepted as fact.
An example that comes quickly to mind is in the Voyager episode, "The Voyager Conspiracy." In it, Seven states many conspiracies she believes are going on. Obviosuly, as viewers, we know those conspiracies are not correct, but Seven, the character, believes they are. But, according to your logic, since she states it aloud on screen, it should be cannon that it's correct.