Point vs. Counter Point: FBI and back door/wiretapping

If you read my post again you'll see I said nothing to the contrary. In fact I wholeheartedly agree with what you say and your arguments support my points:
Everything that applies to closed source code applies equally to Windows XP and to Windows 7. The changes in NT 6.* like kernel self-protection and hardening of internal components against tampering weren't motivated by some government conspiracy. Ultimately they didn't change a thing in terms of how hard it would be to hide a backdoor. But they make a huge difference in terms of security for the end user.

On thing I have to add however: A binary blob isn't a blackbox. Since there are so much more users of Windows than of any other software system on the planet quite a few of them will have the means to reverse engineer interesting parts of the code, analyse network traffic or even cryptographic subsystems.
It's harder without the sourcecode but every backdoor, intentional or by accident can be detected. Independently reported vulnerabilities and yes even malwares, the more advanced rootkits, are the best proof that Windows code too is audited, analysed, reversed and hacked at.

By that I'm referring to the problem that todays systems are insecure by design. We rely on patching, finding flaws, fixing them before the bad guys find the hole and get in. This is a conceptual problem. But given the threat model of average users and businesses the security is more often than not adequate or "good enough".
The user is the major part of the equation as I've now repeatedly stressed.