Cruise prices operate on a yield management basis - the more they sell the more the price goes up. Prices can change on a daily [if not hourly] basis. So yes, the top end prices in the brochures are potentially the maximum that cabin could be sold for, therefore it is valid to display them.
Once again our Newbury columnist is spot on. The trick is to know what the actual going rate should be and not be fooled by "50% off" and the like. When you have been looking at the market for some time it is easy to see what is genuine and what is a come on and whether the price will ever reach that top one. If you are not used to cruise prices then one is more apt to be taken in. But your point is a valid point and the cruise lines do skate close to the wind....Id.