I think a lot more people don't grasp black and white photographs than will admit to it.
When I was in junior high school and was just beginning photography, I shot in black and white. When I got away from photography for a while, I shot in color (C-41) as a hobbyist. When I got serious about photography
later in life, I shot Fuji RVP (E-6) and developed it myself. Then the digital revolution began; it didn't interest me and still doesn't, at least not enough to invest in a serious digital camera (or even a non-serious digital camera, as I am still 100% film based). Later on, I began to shoot & develop black and white again, which I am still doing. When I want to work in color nowadays, I shoot & develop my own Fuji Pro 400H rather than Fuji Velvia.
For me, black and white was an acquired taste. Now I actually prefer it to color imagery. B&W is a more reflective and insightful way of making and looking at (evaluating) images. It requires a different mindset, a different photographic worldview and aesthetic. It requires the viewer of the photograph(s) to "look deeper," for lack of a better term.
By comparison, color images seem to be more of a "what you see is what you get" presentation. The palette of color preoccupies the viewer, distracting them from the deeper implications and undercurrents present in the photograph. Color images are somehow less thought provoking and are easier to look at in a more superficial way; color can readily lend itself to
looking but not
seeing (though it doesn't have to). No doubt many here will disagree, but that has been my personal experience. As always, YMMV.
IMHO, advertising, movies and television has created a mass epidemic of visually ADHD people in our world. Everything has to be "exciting." Everything has to be attention grabbing. Still photographs are thought to be static, placid and "boring." Video is flashy, dramatic, astonishing, stimulating. When fed an incessant visual diet of frenzied activity, garish color and splashing, exploding visual effects, people become visually overstimulated which leads to desensitization. In order to trump the last commercial, TV program or movie (or Photoshopped print), viewers have to be infused with ever increasing doses of visual overstimulation.
This is the antithesis of black and white imagery, which is inherently more quieting, insightful and reflective in nature - to me, at least.
The above is my take on the question of "Do most people 'get' black and white photography?" This is just my experience - YMMV.
Regarding what to say to people who ask why you photograph in black and white instead of color, I think this quote from Ted Grant says it nicely:
“When you photograph people in color, you photograph their clothes. But when you photograph people in Black and white, you photograph their souls!”
This viewpoint is applicable to landscape, travel, nature or any non-people genre of photography, IMO.