"Cruise lines operate the same way most all retailers do, whether selling a travel product or some other type of consumer product. Pricing fluctuations based on consumer demand is at the foundation of a free market society. When demand is greater, prices typically go up and when it is softer, prices go down, whether we're talking about cruises, hotel rooms, tour packages, electronics, books, toys and so on -- the list is endless -- and in none of these categories does the retailer seek out the consumer who has already made a purchase to offer reimbursement if the price goes down."
Oh, if only politicians could learn a lesson in directness from this reply!
Neither Royal Caribbean nor NCL responded to our request for information. However, we suspect that Carnival's answer pretty much states the case for the industry. By the same token, when a price reduction is called to the attention of travel agents, they will usually honor the more recent, lower rate. However, for those who book their cruises through travel agents, it is important to get a guarantee from the agent that they will adjust fares to equal revised pricing. Some more service-oriented agencies will check out revised prices at least when final payment is due, and just before the cruise line's sales department closes out that sailing. Even after final payment, it is often possible to get the difference credited to the guest's onboard account -- which is also usually faster than getting a refund by check or credit card adjustment.
Regardless, knowing that the cruise lines are not likely to be forthcoming on volunteering late-term discounts, prudent cruisers should, at the time of final payment, and three weeks prior to departure, do their own research to check for better rates, and contact their agent or the cruise line directly.