That is a fascinating whole other area of discussion. There are always bound to be some (many?) passengers with enough understanding and interest in air travel to understand speeds, altitudes and headings. With that information they can determine, if interested, where they are at all times during the flight.
In fact, many airlines had this data available to first class passengers at different times.
After 911, is it not obvious that the passengers are not just passive cargo, but a source of potential help. Remember Flight 93?
I remember the story recently about an Air Force Crewman flying civilian across the Pacific. It happened that his usual job was refueling other aircraft in flight, and he noticed a major fuel leak by just looking out his window, and he informed the crew. The flight would have never reached its destination.
In short, if the passengers had flight information as they travel, it is almost certain that someone would question a major deviation like this controversial one, long before a 150 mile overshoot.
indeed, the lack of reports on comments from the passenger cabin is in itself rather odd. It is a perfectly logical second source of media drama. Frequent or attentive travelers surely knew they were not descending on time and asked flight crew.