No, brushed and polished are different. If your intent is to have a mirror type polished finish that looks like a chrome automobile bumper then you will need to use a polish and a felt type buffing wheel. This also removes material but not as agressive as the scotchbrite wheel. You will want to maintain all the sharp corners and edges and not round them. You can search on this forum for "buffed" Lugers to see what they look like.
To be honest I have never seen a black one first hand, only in pictures. From a cost standpoint I would have to say that they are both the same. The parts on these stainless lugers were cast, i.e. the molten stainless was poured into a mold. Not sure which process they used but they came out with a rough finish. They were then probably bead blasted to make the surface uniform and all the raised areas were given a brushed finish. It would cost considerably more to go into all the nooks and crannies and polish them out. So based on that I would say they are the same.
The brushed finish has a directional "grain" to it typically all running in one direction. An example of the brushed finish is like the stainless steel Smith & Wesson revolvers.
If the black finish was removed you most likely will not have a polished finish. The chemical process probably etches the base metal some what. You would probably have to go and do some buffing/polishing.
There is a black on on GB but the pics are not real clear. That one looks like it was painted though. Here's the link...
Black Stoeger Luger