It's also possible, if we assume the other ships raised shields before just getting hit, that Enterprise survived simply because she was the newest, most advanced ship.
This is the horse I'd bet on. Remember that the
Kelvin was likewise surprised, did manage to raise shields in time, and then succumbed so easily that the bridge crew was shouting "Did we even get the shields up!?" to each other.
Elsewhere in Trek, shield strength doesn't seem to increase constantly, or in leaps and bounds, within two-decade timespans. It's possible the
Truman had shields similar to those of the
Kelvin, and that Nero destroyed both the same way, by launching half a dozen initial missiles to cripple the enemy despite shields, and then finishing her off. And it's quite possible that the
Enterprise survived for a crucial extra minute that allowed Nero to have a look at her pennants,
and weathered the first volley better than the
Kelvin and thus was a useful Starfleet asset again very soon after the battle.
It's also perfectly possible that the
Truman and her little flotilla emerged from warp with shields up; dialogue doesn't contradict that, it merely hints at the possibility that Pike
might have dropped from warp shields down without Kirk's intervention. And even there, odds are that Pike would have raised shields, just in case.
It's probable she was designed with Nerada's attack on the Kelvin in mind - those pulse phasers very effectively cleared the way for the Jellyfish's ram attack at the end.
But note that the
Kelvin's full arsenal also nicely intercepted all of Nero's missiles aimed at the fleeing shuttles. Perhaps there's no quantum leap in weapons technology or strength or numbers - perhaps the main difference was that Robau didn't employ the full arsenal of his ship effectively in the first attack. Note that only George Kirk uses those white pulse-guns, and that the ship under his command fires more of the red beams.
I hesitate to think that Starfleet actually did anything directly in response to the
Narada. They didn't seem to believe in this enemy much when actually confronted with it; perhaps the reports of the
Kelvin survivors had been less than accurate, and possibly even less than credible? And if the
Enterprise, Pike's baby, was designed with a specific opponent in mind, why didn't Pike know more about this opponent?
But why did the missiles not destroy the Kelvin in the first shot? They were firing to disable. Why not in the second attack, after Robau gets killed?
I'd speculate Nero was concentrating on stopping the witnesses from leaving in the shuttles, and aiming most of his second-volley missiles at those small craft. Fighting the
Kelvin would be a breeze, but hunting down 20 individual small craft (no matter how small and weak) would be difficult for his lumbering monstrosity of a spacecraft. Better kill all of them as they were still clustered...
Timo Saloniemi