They've said that it's the same timeline up until Nero appears in the past. They later made it StarTrek 'cannon' that timelines simply diverge with time travel (meaning that the rest of the Universe just continued on when Spock/Nero disapeared in the future. This is so it would not alter everything else but simply create a new alternate reality/timeline in the past.
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Roberto Orci: It is the reason why some things are different, but not everything is different. Not everything is inconsistent with what might have actually happened, in canon. Some of the things that seem that they are totally different, I will argue, once the film comes out, fall well within what could have been the non-time travel version of this move.
TrekMovie.com: So, for example, Kirk is different, because his back story has totally changed, in that his parents
and all that. But you are saying that maybe Scotty or Spocks back story would not be affected by that change?
Roberto Orci: Right.
Anthony: Does the time travel explain why the Enterprise looks different and why it is being built in Riverside Iowa?
TrekMovie.com: Yes, and yes.
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JJ: The notion that when this one character arrived Nero that basically the timeline is altered at that moment. So everything forward is essentially an alternative timeline. That is not to say that everything that happened in the original series doesnt exist. I think as a fan the movies and shows, if someone told me that as a beloved thing for me was gone, I would be upset. But we didnt do that. We are not saying that what happened in that original series wasnt good, true, valid, righteous and real. We are not rejecting that. That to me would have been a big mistake. We are simply saying that from this moment in the opening scene of the movie, that everything people knew of Star Trek splits off into another timeline.
http://trekmovie.com/2011/12/22/jj-...ect-plus-talks-alternative-v-prime-timelines/