at worst, they don't even take our mineral contributions into consideration; they just use their local water plussed up with just enough phosporic acid, calcium chloride and/or gypsum to get it to convert. Then who knows what style that would match?
I believe the statement above is most likely the truth. If I was producing malt extract on a massive scale, I'd be using whatever water was available locally, plus the cheapest of pH control, whichever chemical that is (I'm not sure which -- gypsum? phosphoric?). To figure that they'd do anything different with salt additions or softeners in an attempt to emulate the most likely style that their extract would be used for, or even a middle of the road average, is... extremely unlikely.
I shall continue to advocate always the use of distilled water for most extract brewing, just as brewinhard stated originally. The only exceptions are where you might be brewing a style known for its hard water or firm bitterness (IPA, anyone?). Other than that, stick with distilled and let the extract give you a somewhat ordinary level of minerals automatically. Because you really probably don't want to know what crap water they used to make the extract, much less add more minerals on top of it!
My humble opinions. Cheers.