I love old black and white movies. Films like Casablanca or Citizen Kane just wouldn't be the same had they been made in colour. These films were black and white because that was the level of technology of those times. But when you stand back and look at these films you can see that because the colour is stripped away they have in a sense become timeless and when viewed there is always something a bit special and different about them.
The same is true of a black and white photograph. A black and white photograph of an old wrinkly woman sitting by her doorstep is timeless, powerful and extremely though provoking. A picture of an old building or a city view in black and white has the same affect. Without colour you tend to look more closely at the subject and see a level of detail and arguably emotion that you may never spot with full colour. As mentioned before depending on the subject a black and white piece of art is essentially timeless.
Nostalgia is time and again the word expressed when these images are viewed. This is why so many people opt for black and white photographs within the home.