Originally Posted by
brandie
I think it has something to do with security for the US capitol. Post 9-11 I believe most flights in and out of DC have armed security on them to prevent hijackings.
It is probably easier to staff for these positions if the armed security flies connections in the US.
The 1250 mile perimeter has absolutely nothing to do with security for the US Capitol, and the restrictions have been eased (many more exemptions), not expanded, since 9/11. The flight length restrictions date to the 1960s when Dulles was built and jet flying began; they are meant to drive long haul traffic to Dulles and reduce noise at DCA on the theory that longer flights will be more loaded with fuel and thus heavier and louder. (Of course, the approaches to the airport pass over some of the wealthiest and most politically-connected residential neighborhoods in the world, especially Old Town Alexandria and Georgetown.)
Read the Wikipedia article (as I did last night to remind myself). It's pretty clear.
There are other DCA-related rules, especially the routing on the river visual approach from the north, that do have to do with security, or "security" depending on your perspective.