Especially since the time travel stuff in previous Trek made sense. ENT, "In a Mirror, Darkly" is the perfect example. The Defiant gets thrown back in time, AND into a parallel universe. Each universe has its own timeline. You can cross between universes (they did it in every Mirror Universe episode, Worf did it in Parallels), you can travel along the timeline of each universe (slingshotting around a sun, what the Borg did in First Contact, etc...), and in special cases, like that ENT episode, you can travel back in time and step into a parallel universe.
Same thing happened in this movie, but Orci just doesn't want it to acknowledge that, although it's so easy and hurts no one.
One thing, though: Does Sarek even know who Spock Prime is? In the actual film, they never met. Was there a deleted scene in which they did encounter each other? If so, do they actually speak, or only pass by? Sarek might have no idea who Spock Prime is, and I doubt Spock would introduce himself as, well, himself. That might cause Sarek too much pain, especially since Spock Prime grew up knowing both parents.