This aside, you're basically trying to write off nirvana's (IMHO excellent) rant using a minor technicality, one of the common features of the discussions here that tends to make my skin crawl.
He's not trying to write anything off and it is a pretty big technicality. nirvana should have omitted that ideological jab to begin with as it was unnecessary and shows his bias for Apple/against Google. Google is more "open source" than Apple in any way that matters, considering Android is currently on devices their competitors (Amazon) are selling. Apple is mostly responsible for WebKit which is commendable and useful but as far as practical considerations go, nobody gives two shits about Darwin.
But yes, engineering should be the focus and people assume the worst with Apple.
Some people sometimes assume the worst of Apple, or Microsoft or Google, or [insert name of company here]. One of the things that can cause strong anti-Apple sentiment are the rabid fanboys (ie. postings like Nirvana's). They paint Apple to be patron saints - and when reality hits (like it did for me with antenna-gate), users are annoyed because of the unrealistic expectations, but also because of the RDF created by Fanboys. For the record, I think Apple have shown the phone industry a thing or two about engineering excellent products while maintaining a strong focus and excellent compromises. I just wish the rabid Fanboys would shut up, or present a balanced view ... it would make Apple a lot easier to respect.
The central tenet was that discourse here is regularly devoid of sound engineering because it tends to be blinded by mindless cultural perceptions of the companies involved in whatever happens to be under discussion. In the case of Apple the expectation is their products are flawless and if not then all hell will be paid on blogs and comment sections everywhere.
Whether or not Darwin is or isn't open source doesn't freaking matter, it was heavily marketed as such back in the sands of time and even if this wasn't the case it doesn't invalidate the central point made in the rant - that just because this device has an Apple logo every popular discussion surrounding it turns to mindless diatribe as a result of non-engineering centric expectations people place on their products, and every engineering-centric party (i.e. hackers) must deal with the whining polluting engineering-centric forums for days every time it happens.
In effect, the complaint is that commenting resembles the squabble of a throng of uninformed consumers rather than the judicious discourse of a forum of engineers.
GNU/Linux is therefore cough nVidia cough completely, 100% open. Thanks for clearing that up. Darwin sux!1!
/sarc