texture
I always think of the textures as being image maps but you are correct you can use procedural shaders(we call them bricks in DS) to get similar results and you can also use images in conjunction with shaders. I've always used the term shaders for networks created within the program. I suppose it can be a term applied to shaders I've just never heard it used that way. When I heard the word texturing used it's always been used in connection with either a 2D or 3D paint program. Something to think about some more...
Pretty much as you do the displacement and diffuse at the same time. I'm still working out the use of alphas in Zbrush. I know it can be done just haven't had chance to watch any tutes on it yet. Specular maps are a separate thing in Zbrush from what I've seen on video tutorials I'm still to try creating them using the process I've seen.I tend to forget about 3d paint programs, since I don't have any. That might be why I think of textures the way I do. As I understand most 3d paint programs, they create things like specular, diffuse, transparency maps etc. from what you are painting. So they create image maps, but they create ones designed specifically for use in 3d that are designed to be combined together.
I've seen that definition even before DS had Shadermixer I've just noticed it more around that time as I was trying to work out what the difference was with some of the terminology like shaders and shader presets.I think DS tends towards the idea of shaders being the network for in the program precisely because you have Shader Mixer, and the way it shares them out. I first ran into shaders in Maya, where it referred to what DS would call the bricks. But now that I realize from some of matt's other posts, that he is using DS, the DS terminology is definitely the way to go.