In Martin Fowler's keynote at RailsConf, he talked about "post-modern languages," which is to say, essentially, languages that are designed with the expectation that other languages will also exist. The idea originally comes from Larry Wall, the creator of Perl. You can generalize the idea out to the Unix ecosystem and contrast the Unix design philosophy -- lots of little programs, each of which does one thing well, and numerous glue languages -- with the Smalltalk philosophy of "everything in the box from the hardware on up conforms to one idea." (Or, as it's been well-termed elsewhere, the idea of "Turtles all the way down.")
I've been thinking about this a lot, because it's an interesting question. Unix is obviously more successful than Smalltalk. On the other hand, look at Apple computers, how much better they are than Windows boxes, how much simpler to use than Linux boxes. Whether Apple is more successful than Microsoft or less so depends on what you think Apple's goal is. I think Apple's a lot more successful than Microsoft. Real artists ship.
But go beyond that -- the iPod / iTunes / iTunes Store triad is as much an example of a very successful closed system as any Mac, maybe more so. I got this idea from Steve Levy in a Boing Boing Get Illuminated! podcast, and it's a damn good idea. Most competitors to the Apple music triad have tackled only one of its three components, and Apple pwned them all. None of them had the elegance, the ease of use, or the tremendous downloads catalog. By packaging everything within one excellent closed system, Apple came into a settled market, turned it upside down, shook it really hard, and picked up all the money that fell out.
And the funny thing is, it's no secret that Steve Jobs is a fan of Smalltalk. Even today, the language used in the development of Mac apps, Objective-C, is this weird hybrid of C and Smalltalk. To some extent the same Smalltalk-esque closed-system philosophy that makes Macs such a pleasure to use is also responsible for the colossal success of the iPod. Like so much with Apple, it ultimately all traces back to Smalltalk. Even Jobs' business models are based on Smalltalk.
So this is a powerful argument in favor of closed systems. On the other hand, the Mac was a lot less useful when it didn't run Unix. That's an argument in favor of post-modern ecologies. I don't know.
Personally, for me, the jury's still out on this one.