Well times have changed, now airlines have sophisticated technology being able to predict passengers buying patterns in the processed call yield management. The idea is that they are trying to sell every seat at the highest possible price.
In the 1970s American Airilnes were trying to work out a way to eliminate charter airlines, who were selling fares at dirt cheap prices why American had half of there plane going empty.
Traditionally vacationers plan their holidays weeks or months in advance and are usually were travelling for more than a week in contrast to business people who usually had to fly last minute and were generally shorter trips.
So while a vacationer fare will have more conditions Saturday night stay, advance purchase etc, the business traveller will pay a higher price with less conditions.
So this is why there are so few stand by fares now available, as airlines are trying to every seat on the plane for the highest possible price.
With yield management an airline can determine how many of each fare is selling based on past history, if a fare class is slow at selling they may release a few cheaper seats to fill up the plane but just leaving enough seats available for those last minute travellers.
Don't despair this is where the internet comes in handy, carefully watch each of the airlines web sites and they will usually advertise fares for places that are not selling so fast. The internet distribution costs are low so you are not having to pay a third party commision.
Another option is to try http://www.priceline.com
where you bid the price you want to pay and hope you get an offer.