Can't see why one would expect the airline to provide transportation to/from the arrival airport and (presumably some time later) the departure airport. That said even if your on a multi leg trip with arrival of leg whatever into DCA and then departure of the next leg of the trip from IAD, you'll also be responsible for your bags. Claiming at DCA, bringing with you to IAD, then re-checking at IAD. The airlines will not "transfer" your bags from one to the other.