Um, OK, that's what I already thought. Spock Prime and Nero going back changed the past.
But apparently THIS TIME the original timeline was left intact somewhere else, because they wanted to change the way Trek did time travel to have their cake and eat it too.
The time travel logic may make more sense from a theoretical standpoint, but it's very different from how Trek had previously done time travel, which is all I was pointing out.
Even though TNG introduced the concept of the multiverse into Star Trek, I don't feel that Trek XI was a 'have their cake and eat it too' change to Trek time travel. Throughout all of Trek, our Heros have gone back for whatever reason, fixed the problem/healed the timeline, then came right back to their time. They haven't (with the exception of Sisko) hung around taking a chance of changing something that would mess up their own time. However, this time Nero is plopped into the Prime U's 2233, 25 years before Prime Spock shows up. There is no way for our Heros to go back and fix the damage done by Nero's not just showing up, but his setting an entirely different chain of event in motion. Thus the creation of the alternate timeline starting in 2233.
Look at it this way, lets say after JJ's run with things, TPTB decide they want to do something with TNG. All they would have to do is have it start with someone from Temporal Affairs detaining or destroying Nero's ship and rescuing Spock Prime before they get pulled into the origianal rift. Prime Universe reset complete, TNG restored. Go from there. All using the same time travel concept that Trek has used all along.