FTFA :

Major carriers scrapped most minimum-stay rules — put in place largely to discourage big-budget corporate travelers from snatching up the cheapest seats — years ago, although a number of airlines have been tightening up restrictions and tacking on fees in recent months as the price of fuel has soared.

Well, the biggest hit is business travelers. Personally, about half my business travel is between 1-2 days, but I don't pay for them so I am not that worried too much. But I can see where they are coming from.