It's a direct response to one of the points you made once, then made again in the reply immediately before the responses were posted.
("why doesn't Opus use the progress bar graphics" ... "Explorer uses the progress bar graphic.")
Like Jon said, as far as we know the images Explorer uses for those graphs are not part of any theme (or at least any documented theme that we're aware of).
They may be private bitmaps within Explorer itself, or part of a private/undocumented theme, or possibly even drawn algorithmically by code within Explorer which is not shared for other programs to use.
It's a bit like asking why the buttons and other elements on Amazon look different to the ones on YouTube.
If you're concerned about programs not using the graphics dictated by the current Windows visual style, you should start with Explorer and/or realise that the style guide and APIs/themes don't handle a lot of situations, with free-space graphs being one of them. (At least as far as I know.)
I haven't looked at that yet, but it's on my list.
(If you don't want your own thread to get derailed and only partially answered, stick to one question per thread. 
)