Every single day very large and important organizations rely on software to keep themselves running (hospitals, infrastructure control, intelligence agencies, the military ... and so on). Yet nearly none of these organizations are legally allowed to see the source code of that software. There is just absolute blind trust in its ability to work correctly and be reliable. Not to mention secure.
Where is the proof this software isn't full of backdoors, vulnerabilities, logic bugs or more. Organizations such as those above need to start asking (demanding) their vendors provide some real proof that the source code or binary was audited by a third party - i.e. not the original developers of the software. This proof works both ways. It gives the company the chance to say "hey - we can't catch all the bugs, but we did our best, and thats why you should choose us over our competition". And customers are given a little more trust in the investment they just made. Because now they know their vendor went further then the competition to produce a better quality product.
Lets take Windows Vista for example - many hackers have audited its source code on while on Microsoft's payroll. This is a good thing, and Microsoft can now say to customers "YES we did audit our code after development". Which is a lot more then most other vendors out there can say. The flip side to this argument is open source. Just because the source is open doesn't mean people have reviewed it for vulnerabilities (download a random sourceforge project and you will understand what I mean). But on the other hand, it does give the customer/user the ability to inspect the software they are relying so heavily on.
How many of you can honestly say the software products your company relies on have been audited by a third party?