Is a telescope a proprietary source? Is a commercially manufactured CCD a proprietary source? Maybe they got the response curve wrong! Okay, test it before you announce your galactic dust measurement paper! I take that attitude towards "experimental mathematics" that involve computers in some deep way.
And no need to patronize with Wikipedia links, I know the story about the Mars Climate Orbiter. And I don't think it even demonstrates your point. As I understand it, vxWorks, which many of the NASA missions use, is closed source. You have to pay to see the source. And I'm sure that Wolfram Research would or could do the same thing for e.g. intelligence agencies (and hopefully will do for everyone in the future, fingers crossed).
Let me do some patronizing of my own: are you sure your understanding of what the language does is up to date? You seem to talk of it as if it were a predominantly a CAS: http://reference.wolfram.com/language/index.html