Perfect examples, Alex.
Airport '75 is a disaster movie.
United 93 is not. If you cannot grok the difference, there's nothing I can do to help.
mousepod is unequivocally wrong.
Titanic, for example, may be many terrible things, but it is not a disaster movie. Mixing plenty of hogwash fiction with remarkable depictions of fact does not change that the disaster really happened. Such a thing cannot be cheesy enough to rise (er, lower) to the level of a Disaster Movie. And believe me,
Titantic tried real hard.