If I recall in a interview with Mark Meer here actually mentioned that scene. He said he did many different versions of that scene with different tones of emotion and found it funny that was what they decided to use.
I think he might have also been referring to the fact that the take they used resulted in a hilarious shift in tone if Steve survives, where it goes from Shepard screaming his name to expressing only the mildest amount of concern in the space of several seconds;
(And dang, been ninja'd by TMK)
As for Vega, I'll admit I wasn't too fond of his character when I first played ME3, but I thought that FPJr did a brilliant job in the role.
Subsequent playthroughs have actually made enjoy his character more. Sure, he often has a degree of chutzpah about him in conversations, but so does Garrus and it shows in how they try to one-up each other when talking about past battles on the Normandy. Vega's his own guy and his interaction with Shepard show that despite his snark, he has a ton of respect for them and considers them the kind of soldier he wants to be?
He's a far better character than Jacob in ME2, who despite being a similarly likeable and easy-going guy, was kinda bland when you got down to it? Sure, people often say the same thing about Kaidan, but at least Vega and Kaidan are memorable, whereas the reaction Jacob tends to garner is... "Oh yeah, he was there too?"