I'm afraid this might be a new trend.
United is announcing a new checked bag policy for customers who purchase nonrefundable domestic economy tickets. Customers purchasing nonrefundable domestic economy tickets who do not have status in Mileage Plus or Star Alliance may check one bag for free and a second bag for a $25 service fee. Customers who have attained Premier status or higher in Mileage Plus or who have Silver status and above with a Star Alliance partner, are exempt from this policy change. This policy is for travel exclusively within the 50 United States, Puerto Rico, U.S. Virgin Islands and Canada and applies to tickets purchased on or after February 4, 2008 for travel on or after May 5, 2008. Please view the Domestic baggage questions for additional details on this policy.