This is simply how Nikon has decided to present things. Frankly, I find it odd and is something I mentioned in my reviews of these cameras.
The reasoning I guess is that HDR is a solution to shooting a backlit subject. That way, you go to backlight mode and either use the normal part which uses the flash to fill-in the foreground or use the HDR part which blends two or three exposures to give you a nicely exposed foreground and background.
The reality is that the camera has no idea if it is the back of the front of something which is much brighter than the rest. HDR is HDR and it will work in scenes without moving subject the same. So, yes, you can use it in non-backlit scenes.