The truth is that most are not "black" and "white" at all. Black and White photography tends to fall into three basic processes; gray scale, bandicoot, and sepia. Then you get colorized that take one of any number of base colors and creates the same look only using a "color".
What is chosen can really change the feel of the final product. And knowing which one to use, or NOT use takes time and experience. Here are three examples of what I am talking about. When people look at these images ALONE, they think "black and white", but as you can see there are very distinct differences between them.
Gray Scale (the first image below) will tend to give off a blueish light (but not always), Bandicoot (the second) looks much like Gray Scale but "dirty", and then you get Sepia (the last) which is really brown tones. Sepia, as well as the others can be dialed up or toned down as well, to create the desired feel. But again, knowing when to use each, and how MUCH of it to use is very important.
When I do a shoot, I discuss with my clients what their likes and dislikes are concerning processing. And some images lend themselves to one method over the other. I will generally go through the "from camera" files and determine what ones are best and how best to process them given the customers desires and an artistic eye without OVER processing the images.
(NOTE:This is just a general overview to demonstrate processing differences. There is of course more to this than what I posted but it is not needed to demonstrate the basic information presented.)