The Wright Amendment (WA) was put into place to protect DFW. It is named after fomer congressman Wright. Basically the WA stated that no aircraft of more than 56 seats may fly from Love Field to any state that does not border Texas. It has since been amended to include a couple of other states as well.

Southwest kinda gets around it by flying from Love Field to a bunch of airports in adjoining states. From those airports, pax can then fly a different flight to anywhere in the Southwest system. However, the flights must be purchased seperately. Southwest cannot sell them as a connection. So if you wanted to go DAL-LAS, you would need to buy a DAL-ABQ ticket and a ABQ-LAS ticket. This is not as cost effective as a DAL-LAS ticket would be.

In reading the PlaneBusiness BB (http://www.planebusiness.com/cgi-bin/ultimate.cgi), the prevailing opinion there is that the WA will eventually be repealed. Once that happens, Southwest will flood the Dallas market with low cost flights across the country.