Pieter Hintjens has uploaded on vimeo the talk on ZeroMQ and open source he gave at CERN on 27 June 2013. I warmly suggest you to watch it. It is longish, but it is worthy.
He says ZeroMQ is designed around a protocol, that originally was just about framing the message sent around, and then it expanded adding versioning information and security.
Than he says how important are patterns (Pub-Sub, Req-Rep, Pipeline ...) that are wrapped in sockets, giving an easy to use approach, and robustness, to the framework.
Bindings are important, because they make ZeroMq available on many different platforms, and they help building a strong programming community. As it helps the licensing policy, designed expressly to take advantage of the open source market.
The ZeroMQ's growth is based on contributions, anyone could contribute with its own code (through github pull request). But you should not break the API. The process is based on small changes, that should lead to a smooth migration to new versions.
A strong point is that people are more important than the code. The idea is that a project is a way of organizing people around a problem, so that they can interact to find solutions. Problems are important, because they lead to improvement.