At the end of FoTR (the book), it says: "Here ends the first part of the
War of the Ring. The second part is called the Two
Towers, since the
events recounted in it are dominated by
Orthanc, the citidel of
Saruman, and the
fortress of
Minas Morgul that guards the secret entrance to
Mordor."
Now it could well be that this quote was generated by the publisher and not
Tolkien (that it my belief). This was debated on a thread a while back and, if memory serves, someone quoted Tolkien in Letters as saying it should have referred to Orthanc and
Cirith Ungol (I may be wrong on this and will glady accept a correction - my recall ain't what it used to be).
I originally thought Cirith Ungol would have been correct but, after thinking about it, maybe Minas Morgul makes more sense. Certainly many more chapters were directly affected by the
Witch King's citadel if you include the
Faramir episodes.
As for the movie, I guess PJ is trying to simplify things.