I understand the benefits, mentioned by the commenters to my last post, of the “Unix Bargain” that Apple struck when it bought NeXT.
I’m very happy about what it’s done for the platform:
The vastly improved underpinnings (fewer crashes, etc.) have prevented a complete exodus to Windows.
The ports of Unix-based developer infrastructure have allowed Macintosh developers to be more productive.
But my unease remains, so here’s my second attempt to explain why.
The way I see it, the reason the Mac received a Unix graft isn’t because it’s somehow the best of all possible worlds to piggyback on another platform, a platform with wildly different assumptions about its user base. It is because the Mac doesn’t have the marketshare to pay for or attract these benefits otherwise.
The tendency to think of the current situation as nirvana, rather than a compromise, blinds people to the costs of the compromise.
A parting thought I’ll come back to later: the Macintosh is not Unix with a pretty GUI on top. The more developers think like that, the more chance there is that OS X becomes just another Linux variant that happens to costs $129.
1/6: Edited for clarity
Weaponized Fluff 
I don’t see the Mac as ” Unix with a pretty GUI on top”, but I can understand some people see it that way, and I’m fine with that.
As I wrote yesterday, I’m a mac user first. In my job, I use ProTools, Logic, Final Cut Pro, etc. (Not Bash ;). And no UNIX ever had those applications before or even have something equal now.
I don’t think it’s the nirvana, but I don’t think neither it’s a compromise nor a “bargain”. It’s the best choice that Apple could have made. As when I work in audio with analog and digital peripherals, I want to have the best of both world.
Maybe some people just see Macs as “Unix with a pretty GUI on top”, and maybe more in the developers than other users, but would they use Macs if there was no UNIX under the hood? I think they are people coming “on top” of the “classic” Mac user base.
It’s true that this lead to a Mac user base including radically different types of people and I think it’s good.
I may be biased, but I see more interesting apps with a real Mac GUI now than in the pre-OS X days, an a lot of them are even free.
It’s in Apple’s hands to stay focus and give us the “Mac experience”.
IMHO, they made a fairly good job hiding the BSD layer to those who don’t want to see it, although, they should focus a bit more on HGI and consistency in OS X and in their own apps (and specially the Finder!). That worries me a bit.
I think you’re overreacting here.
Saying that the Mac lacked the market share to attract or create the benefits of Unix is ridiculous: the famous other platform with so much market share does not seem interested in creating Unix-like benefits for their customers, nor are they clever enough to simply take them outright. Apple’s engineers are very smart–smart enough to not want to reinvent the wheel, and smart enough to be willing to work around the rough edges of someone else’s invention and make it their own. The whole point of BSD and open source in general is that we waste far too much time on the not-invented-here syndrome, and that this wasted time is a huge barrier to progress.
I also completely agree with Fred B: the apps these days are much more interesting and complete, and often free. Some developers are naturally better at designing UIs and some are better at writing code that does particular work; few are expert at both. Having such a separation in the OS itself enables these two families to live together harmoniously. Compare the UI of Fetch to that of Transmit, which relies on Unix staple ncftp to actually do the fetching. I look back at my Windows and BeOS days, and what you had was essentially a shareware development community trying to live fat on lame text editors and music players. With OS X, you have companies like Panic and Omni producing useful, inventive, well-designed apps for a small fee, and a large community of open-source folk producing good apps perhaps lacking that final polish, but at least usually adhering to some degree of standardization. It’s never perfect but I think now we’re much closer to cohesion than we were when crap like Quark could get away with being completely un-user friendly.
I agree, the Mac is definitely more than the sum of Unix and Aqua. The difference I think is largely that of culture and taste, concepts which no doubt seem odd to those developers who are not a part of it. But I don’t think that you should consider an influx of Unix likely to result in a derailment of these values. It hasn’t happened yet, and the Mac can’t really become “more Unix” than it is right now.