As Mike pointed out, the only compensation for a cancelled cruise, in addition to a full refund of the fare, is a discount on a future cruise. This is customary throughout the industry as a gesture of good will. There's no requirement, either in the passage contract or under any applicable law, to provide any other compensation. Cruise lines have the right to cancel -- or to terminate -- any cruise for any reason at any time, with no obligation other than to refund the fare (or the prorated portion of the fare in case of early termination).
If your cruise booking included flights, a land tour, or a hotel stay , Princess Cruises cancelled the reservations and your refund is for the entire price of your package. If you booked any of these on your own, it was your responsibility to cancel the respective reservations before any applicable deadline and any refund is a separate matter between you and the respective airline, tour operator, or hotel.