Despite our differences in social upbringing, nationality, language, religion, etc... We all agree in 1 thing, that Die Hard is a Christmas Movie, right?
Yippee Kay Yay... (The only movie that doesn't depresses me in Xmas)
The set up for the plot is that everyone is at a holiday party, in addition the cops were slow to respond because of the holiday (Hans Gruber planned for this). Without xmas, the date of the attack would have been different and a special someone whould not have been in the building either.