Applications like the one mentioned above have been emerging from various corners of the industry over the last five or so years. I have little use for them as my personal work is mostly about creating and recording new material but there are a lot of folks out there ('musicians' that are not not themselves players of instruments) that live off of isolating and sampling existing parts and mashing them together to "create" new music. Since I have no need for such a tool, I have not looked into how they actually accomplish what they claim. I do know that they are not simply checking the stereo phase as simpler "vocal scrubbing" or karaoke programs and plugins have. There's a bit more to it than that. I do know that these tools are widely in use. I had thought by now that one of these would be offered as a free plugin to one of my DAW's so that I could play with it but, no, hasn't happened. I can see these tools being used as transcription aides.
Roland offers a product called R-Mix which appears to take a pre-recorded piece and use the tools to separate it out into tracks so that it looks like it may have when recorded, isolating each part, and allowing you to edit you heart out either remixing or pirating parts, changing tempo, key, etc. It costs about $200 US. You can look at a demo of R-Mix here.
The underlying software components are now appearing in several Roland offerings (sampling workstations) so I continue to assume tools like these will be embedded in DAW's in the near future just as their V-Vocal software has.