Not sure if we are totally missing out as I see at least one token MD80 flight to DFW when looking at a mid June schedule. I think the larger driver here is the shift from the 50 seat RJ's like the CRJ 200's and ERJ 145's to the larger RJ's such as the CRJ 900 and Embraer 175's. Looking again at mid June, the bulk of LR flights shift to CRJ 700's and 900's acquired from the US Airways merger. With AA bringing a ton of CR9's and ER175's on property later this year, much of the flow to/from short haul locations to the major hubs will be seeing this shift.
As a former frequent traveler between LIT and IAH, I expect United to start dropping frequencies to LIT in favor of the larger RJ's once Skywest/Express Jet start taking delivery of their first batch of ER175's later this year. While I know I'm in the minority, I'm really going to miss the ERJ 145's on United and AA between LIT and IAH, DFW, and ORD. One of the best rides for the business traveler flying solo out there.