Iron Man 3, Die Hard, The Lion The Witch and the Wardrobe etc. are not Christmas movies. They are movies related to Christmas and/or are set at Christmas.
A Christmas movie is a movie with the central theme about Christmas related notions, like presents (Jingle all the Way) or Father Christmas (Santa Clause), not terrorists (Die Hard) and superheroes (Iron Man 3).
This whole idea of including films like Die Hard into Christmas movie lists was all thought up because of the fact that morons can't produce a list of 10 Christmas movies, so they need to stretch the rules and include films that aren't related to the genre of Christmas.