There's been a bit of revolution in OpenBSD as well, just smaller ones. OpenSSH, PF, and now LibreSSL were all fairly rapidly developed at inception due to issu

There's been a bit of revolution in OpenBSD as well, just smaller ones. OpenSSH, PF, and now LibreSSL were all fairly rapidly developed at inception due to issues with the original projects they replaced. They made it into the base system within 1 or 2 releases (every 6 months in OpenBSD), so there's no reticence to change or rapid development. However, they did take care to limit the projects to a well understood, readily achievable scope thus allowing them to ship on time (what a novel concept in software development!). OpenBSD also pioneered some major concepts in modern OS design such as privilege separation which has since been adopted by most other comparable operating systems. Yes, they do an excellent job of maintaining consistency, but a lot of that has to do with good design and careful choices, and not because they've avoided change.