Besides which...who's to say Romulus isn't destroyed in STO?  If you've been keeping up with their projected history, there are technically 2 Romulan Empires.  Of course, STO says that the Klingons go to war against the Federation...under MARTOK.  I call bull.  STO is gonna be crap, especially when they decide to "hot rod" a Sovvie to be their flagship and apparently the Klingons dug up a 22nd century ship as their new primary ship.  Sorry, STO gets two big thumbs down as far as story.
And remember guys, both Nero and Soran have the Khan-like madness going against what should be logic here.  But Nero lost his home, his family, and probably a good deal of his friends.
As for his vendetta, it likely starts with Vulcan because of Spock's involvement.  Whether it's Spock's action or inaction, or perhaps Vulcan/Starfleet's lack of action, that results in Romulus's destruction, either way Nero would have a clear reason to go after Spock's home.  I think someone on TrekMovie.com put it best though: "Romulus goes BOOM?!? Talk about taking things personally - this guy makes Soran look like a Red Cross worker."