Not defending them in the least, but Nigel, you're wrong on the fact that it's illegal.

Check various tourist hotspots and you will see price variances due to a huge demand for a facility vs. not enough accomodations.

For example Las Vegas has hotel rooms that are extremely high during the winter/spring and they are much lower in the summer. Rationale, who wants to go to Vegas in the summer.

Another example would be Ski Resorts. Is there a reason that a hotel room is 1/2 the price during the summer than the winter. You bet - no snow.

Airlines also practice this as well as gas companies. Ever notice how gas prices go up during the Labor Day/Memorial Day, 4th of July, Thanksgiving, etc? It's not illegal.