I don't know if this adds anything beyond the marketing / competition pieces discussed above, but DFW - SNA is more than 200 miles shorter than DFW - SFO/OAK/SMF flights (reflected in flight durations as well.)

DFW - SFO = 1463
DFW - OAK = 1455
DFW - SJC = 1437
DFW - SMF = 1429
DFW - SNA = 1203

I also find it interesting that the morning flights SNA - DFW are 3:05 mostly, but the afternoon flights are about 2:57 in the schedules. Maybe the hotter afternoon air is less dense, so the aircraft flies faster due to decreased rag? Or does the flight duration difference justify serving a simple snack, instead of a meal?