I'm really not quite sure how someone could draw irony out of that scene. I mean, c'mon, his son just had a whole buncha gangsters go all "Bonnie & Clyde" on him. Like someone above said, I don't care how ruthless you are, if you see your first son (or second or third or fourth for that matter), in the state Santino was in (dead, full of holes, no less), you're gonna be in shock, and really upset. But in my opinion, Vito did a fantastic job keeping his true feelings in check, and maintaining his composure. Although in the book, it says that at one point, Vito grabbed hold of Bonasera's shoulder to keep himself from falling, which is a sure sign that he was distraught.