I think a lot of visitors don't visit the residential areas of the city. The museums and the monuments are mostly at the National Mall and downtown. Of the more residential areas that get visited are Dupont Circle and Georgetown, but mainly for the restaurants and the shopping, not to wander the streets and look at houses.
Pretty details and pretty flowers:
Personally, I think the townhouses in DC are one of the best things about the city, and it saddens me that there could be even more of them left, but many were mowed down in the 1950s to make room for larger buildings. Then again, I guess there had to be more space for offices - a three story townhouse couldn't really hold that many offices! In any case, Washington, DC was spared a lot of the demolition that destroyed many American cities, leaving them with large office buildings and no night life. DC offers many great neighborhoods and lots of pretty houses.
One of the prettiest blocks in the city is the 1400 block of Q Street NW (DC is on a grid so it is easy to find - it is the block of Q Street that runs between 14th and 15th Street NW.) The houses are quite varied and some are set a lot further back than most townhouses, with beautiful gardens in the front. I am a city girl but one of the best things with DC is the many beautiful gardens brightening up the streets. If you ever visit, make sure to check it out! Take the metro to Dupont Circle, exit to Q Street and walk the five blocks to see this charming street.