One useful effect of funneling the discount flyer into off-peak periods is that it reduces rush-hour strain on airport facilities, currently the biggest bottleneck in the system.
Where wacko pricing becomes totally exasperating is when flights aren't selling as projected and airlines post surprise discounts at the last minute, hoping travel agents will funnel passengers onto an undersold plane. This may result in a discount traveler who has studiously abided by many paragraphs of rules--paying for his ticket with Treasury bonds in the presence of a notary public--getting the same deal as someone who waltzed up 10 minutes before departure. Such "blue light specials" have a component of business logic but cannot help making consumers feel ripped off.
The dawn of deregulated fares has taught an interesting lesson, namely that air travelers catch on to kinks in the system quickly. In the kind of theoretical markets economists postulate, consumers exploit corporations as much as vice versa. Real markets rarely clear so elegantly, partly because consumers often lack enough information to figure out who has the best terms. But in the airline business, information flows at the speed of light, or at least of newspaper advertising. Few bargains go unnoticed.
Last winter American Airlines was puzzled when some buyers of a particular class of SuperSaver were using just one segment of their tickets and throwing the other away. It turned out that restrictions had been written in such a way that flyers came out ahead by buying two round trips and using half of each.