Okay, just to stir the pot a little.
There has been a theory floating around various Trek discussion forums, including this one, that OldSpock and Nero may not be from the original universe that we know and love (despite what the writers would have us believe). I am a very vocal proponent of this theory. And there are several reasons for this. First, we know what TNG-era 24th century Romulans look like.
This is a TNG-era Romulan.
And we also know what Nero and his fellow Abramsverse Rommies look like.
This is Nero.
Notice the differences? TNG Rommies have hair. They also have very pronounced eyebrow and forhead ridges. Abramsverse Rommies are bald and tatooed. Horatio calls them "Tatoomulans". That sounds appropriate. Notice also that Nero has no eyebrow or forehead ridges. In fact, the only thing that the Abramsverse Rommies have in common with the original universe versions is their pointy ears. And even those aren't exactly right.
Then there's the Narada. Again, we know what Romulan starships look like.
This is a TNG-era Warbird.
We know from TNG and the TNG-era movies what the 24th century Romulan design aesthetic is. The Narada follows none of the design parameters of the established 24th century Romulan designs. I know that according to "Countdown", the Narada is supposedly Borgified. But that is not established in the movie. According to the on screen dialogue, the Narada "is a simple mining vessel". If that is the case, then why is it five times as big as a warbird and more powerful?
Based on these obvious differences, I would have to surmise that Nero and OldSpock are not from the original TOS/TNG universe that we know. They are probably from a similar, yet slightly different alternate universe where Romulans evolved without eyebrow ridges, developed an affinity for Darth Maul facial tatoos, and applied their technology to the mining industry rather than the military. This would explain why they didn't have the technology to stop the star from destroying their planet and needed help from the more technologically advanced Vulcans and Federation.
Considering that Romulans of the 24th century TNG-era can make their own artificial black holes to power their starships, it would stand to reason that they would not need Spock to take out the supernova. They were technologically advanced enough to do it themselves.
This is all just a theory which seems to fit the facts (as seen on screen). I tend to agree with this. It makes sense. To me, there's no way that "our" Spock would allow his home planet to be destroyed. However, OldSpock is probably intellegent enough to know that he came through the black hole/temporal whatchamajigger into an alternate universe and that the Vulcan that was destroyed wasn't "his" home world. That's probably why he wasn't too keen on slingshotting around the sun and fixing everyghing. We know he knew how to do it. Unless, of course, this Spock had never done that maneuver in his universe??? Hmmmm. We may never know.
I know. I just love to stir the pot.
Note: Unfortunately, the pics won't show if you're not logged in to startrekmovie.com at the same time. Sorry. If this forum would let me post pics from my hard drive like startrekmovie.com does, you would be able to see what the heck I'm talking about.