The article states:
Washington, D.C. Long-haul flights are prohibited at American's Washington, D.C. hub,
Doesn't specifically mention DCA, but DCA is an American hub.
AA has flights out of IAD - just that they have continued to cut them and a few years back closed the AA Club at IAD.
When AA picked up DCA-SAN with the merger with US, they moved that slot to a second DCA-LAX, and cancelled one of its IAD-LAX fights.
Not sure if AA is flying any flights out of IAD? Maybe the redeye from LAX.
DC has three airports like NYC. DCA, IAD, BWI. None are in Wash DC. DCA is in Arlington VA, and Dulles is what used to be Herndon-Sterling, now called Dulles.
No reason AA could not do more flights out of IAD but doesn't make sense with East Coast connections at DCA, and PHL being an international hub.
DCA is a good hub -but expensive domestic flights on non-stop, along with an affluent area - where people will buy F, as well as business travelers.