You are reframing my post as an OSS vs. the world debate, which I'm frankly not interested in having. You should always shy away from phrases like "You sound as if..". And yes, I'm quite aware that Darwin is the underlying core of OSX. Are you aware of the current hits Apple is taking from OSS advocates / Tom Yager on the supposed closing of Darwin? http://www.infoworld.com/article/06/05/17/78300_21OPcurve_1.html
Thinking that OSS is what drives Apple to innovate seems a bit specious to me. Apple was driving innovations in the computer market well before the concept of Open Source had any kind of widespread traction. I feel pretty confident in stating that if every OSX open-source app dropped off the radar tomorrow, Apple would continue improving it's home-grown apps. Perhaps even adding tabs to iChat.
While I disagree that simply having alternatives does anything to affect a given market (eg: having Yugos available does nothing for the innovations in Minis, even though they're both compact cars), that wasn't the point of my post in the first place. My point was: why include all of these me-too OSS projects that are doing little or nothing to drive their particular categories forward while glossing over the large number of OSS apps and tools that provide unique functionality readers may not even know are available.
As for tabs being a unique feature: I think an argument could be made there, but again, that wasn't really my point. My point was that there is already a 3rd-party solution from a small developer that offers this. Apple may be making a conscious decision to *not* include them and crush the small 3rd-party developer. Especially since they've been accused of doing just that in the past. Ultimately Apple doesn't really need to continue updating programs like iChat, iPhoto, et. al. to be cutting edge tools. These tools are designed to be given away, remember.