Actually, Midway is anything but a commuter carrier. Yes, they fly CRJ's, but they have no EMB-145's. They still have F-100's, and they have 737-700's on order that they will start getting this spring.
That is not the case at all. True JI has ordered CRJ-200s, but the airline found the A320 to be uneconomical and cancelled its order for 4 a/c. Consequently 15 737-700s were ordered to replace the F100s and provide for expansion. 2 further were ordered from lessors and these aircraft(N311/2ML) were just delivered.