James at 2010-05-08 13:41:28:
"Here's the key scene in the movie that handles their discord:"
I'm not sure that's the "key" scene. The conflict is set up long before this. Yes, that scene is the culmination of their problem -- however:
The opening scene aboard the airplane, we find out that 1) John McClain is afraid of flying. 2) He is flying to LA because his wife works there. 3) John is a New York cop. Right away we get a sense something is wrong with the relationship.
John also scopes out chicks every chance he gets.
There's also a GREAT scene that sets up their "ununion" as John first sets foot in the building -- when McClain arrives he looks his wife up in the computer system as Holly McClain, but can't find her. She is using her maiden name, Genero. Now, we know something is really up! Not to mention her using her maiden is later paid off with the bad guys when her real name is revealed.
The scene quoted in the OP is the exposition so the audience can say "Hey, this is why they are estranged." Without the previous scenes setting this up, you couldn't have this scene.
In a movie like Die Hard, I think it's much more important how we get to those expositional scenes (as they are extremely rare in the action genre) rather than what they are saying. It's sort of an obligatory scene to the plot. It's the scene that knock-off movies emulate, forgetting that there is so much more finesse that got them to that scene in the first place.
Just my two cents worth.