This has been discussed a number of times here.
If you book standard cruise line air the cruise line takes no responsibility and acts only as an agent to the airline. Whatever they do in the event of a problem is basically a "favor" to you.
Here are the exceptions: Royal Caribbean's/Celebrity's Choice air program. With Choice air they will do most of what people thought they did with standard cruise air. With Choice Air Plus, and an additional $35, they will provide "concierge" style service in selecting your flights and helping with problems.
Here is the link to the ChoiceAir page on RCI. Air Travel Programs - Royal Caribbean International
Here is the full FAQ for ChoiceAir: http://www.cruisingpower.com/choicea...Air.do#Assured
ChoiceAir is the best "cruise air" program. Other cruise lines are not obligated to do anything other than get your flight.
Here is Holland America's policy:
"Holland America in arranging for the transportation of guests to and from the ship, does so with independent contractors and only as a convenience to the guests.
Holland America is NOT responsible for incidents such as airline cancellations, reroutings or any disruption of scheduled services or accommodations."