Actually if the act of an object exiting the Black Hole/Lightning Storm/whatever creates a branching universe each time, then it happened twice in Star Trek 2009 didn't it? When Nero arrived in 2233. An identical universe to the Prime one was created and continued to be the same, until he interacted with the U.S.S. Kelvin, causing the premature birth of James T. Kirk, who would've been born on Earth had it survived and got back there. Old Spock arriving in 2258, duplicates the universe again. A universe containing all the events up until that point, all the damage Nero did before - who has since escaped imprisonment and is sitting around patiently to intercept Spock. Similar situation, nothing differentiates it until Nero sees and captures Spock. So it's perhaps not a question of time-travel to save Vulcan. BUT universe and time-travel back to the first branch, where Nero is presumably waiting for a Spock who's not coming. Did that extra time spent waiting mean Nero changed his plan? How long was his patience? He wanted to take out Vulcan while Spock watched. Probably even worse for the Federation in that first branch off the universe. After it became clear, he wasn't going to show up, the Narada heads straight to Earth first instead... It's that multiverse theory of both outcomes happening and continuing to move forward, in this case - whether Old Spock exited or not. As well as 25 years before that - the first deviation, whether Nero exited or not.