I noticed this change in the September schedules as well. USAirways will be adding a relatively significant amount of mainline flights out of Columbus and Indianapolis, bringing mainline back to DCA as already mentioned, as well as adding mainline to other routes.
From Indianapolis, PHL will see 2 flights upgraded from RJs to 737-300s and DCA will have 3 RJs bumped up to 733s. The 5 new mainline flights will put Indy's total to 14 daily mainline flights, though 2 RJ flights will be cut (1 from DCA and 1 from CLT) presumably to compensate for the additional mainline seats.
From Columbus, CLT will see the largest increase, going from 4 mainline flights and 1 RJ to 6 mainline flights and 1 RJ. CMH-PHL will also receive an additional mainline frequency, going from 5 to 6 daily flights. A CMH-PIT frequency will be upgraded to an EMB-170 from an ERJ, and one CMH-DCA flight will go from an ERJ to a 733. USAirways' weekly CMH-MCO flight will remain as is with a 733. Overall, CMH will have 10 mainline flights, up from 6, and 28 daily flights total, up from 25.