Yes, residents of Washington, DC should have the right to vote in Presidential and Congressional elections as they are residents of the United States. As such, they should be treated to the same rights that all other citizens of the United States are privileged too, this includes voting in all elections.
It is completely unfair for the people of Washington, DC to be affected by the decisions of the president and congressional officials without being able to voice their opinions and elect the people who control their lives. Any citizens of the United States should have the right to vote no matter where they live. Even citizens living abroad get to vote as long as they remain citizens.