What I got from the Orci interview with TrekMovie is that when Nero travels back in time to destroy the Kelvin (two events that occur within the Trek timeline we're familiar with) the destruction of the Kelvin (an event that didn't occur in "our" timeline) is what creates a second timeline. And this second timeline (which is where most of the movie takes place) is like "ours" in every regard... except for the fact that the Kelvin is destroyed and the repercussions of that have changed things (i.e. Kirk's life is screwed up, the Enterprise is being built in Iowa, etc.).
What Orci was getting at was that we don't need to worry about "our" timeline being screwed up. That is preserved. The destruction of the Kelvin is a catalyst that creates another timeline -- a timeline that is similar, yet different from our own.
By the end of the movie, we don't need to worry about the timeline being restored; certain events have created another, and it is within that timeline where the movie exists. Having Star Trek exist in a new, altered timeline opens the door for things to unfold differently -- even though we'll be seeing those things unfold differently with the same characters we know and love.
It's the best of both worlds: We get to see a Star Trek where things have the potential to unfold in brand new ways, but with the characters we're familiar with. And, ultimately, that had to be the goal of this movie as Orci and Kurtzman were writing it: Putting Star Trek in a place where it doesn't have to be beholden to canon, but preserving the characters we all know.
With this movie, I think they will have done just that. And I can't say I disagree with that choice. It was necessary for Trek's long-term viability. And they didn't have to incorporate the already existing timeline at all. They could've just threw canon to the wind and started over. That they made the effort to justify this movie by honoring the existing timeline shows me that they did, indeed, care. I tip my hat to them for that. We all should. It's more than anybody else would've given us.