Users choose among distributions, and may supplement a distribution by downloading code directly from developer sites. The effect of this tier separation is to create a very fluid internal market for improvements. Developers compete with each other, for the attention of distributors and users, on the quality of their software. Distributors compete for user dollars on the appropriateness of their selection policies, and on the value they can add to the software. A first-order effect of this internal market structure is that no node in the net is indispensible.
Distributors can fail without damaging or compromising the common open-source code base.
The ecology as a whole has a more rapid response to market demands, and more capability to resist shocks and regenerate itself, than any monolithic vendor of a closed-source operating system can possibly muster. Another important effect is to lower overhead and increase efficiency through specialization. No rushing a 1.0 out the door before it's done right. Distributors, on the other hand, get to specialize in the things distributors can do most effectively. Freed of the need to fund massive and ongoing software development just to stay competitive, they can concentrate on system integration, packaging, quality assurance, and service.