It's kinda tongue in cheek, but that's how we say things in my part of the US. "Fourth of July" is spoken of exactly as if it were the name of the day, like "Thanksgiving" or "Christmas". Just like we still refer to "Cinco de Mayo" even though we don't speak Spanish.

Obviously it's not really called "Fourth of July", but nobody ever says "Nth of Month" here otherwise. And I'm kinda grateful as I like "bigger to smaller" notation. Yeah, mm/dd/yyyy sucks, but saying it that way is pretty expressive because the year rarely matters. So it's like "Hours and minutes" or (yeah, sorry Europeans) Feet and inches. Bigger before smaller quickly expresses precise information to our caveman brains. At least to my caveman brain.

Also, the movie really wasn't that good in retrospect, but we had some sort of fever about it because it was expensive with lots of explosions, and good music licensing. And both patriots and antipatriots had something to get out of it because aliens blew up the White House.