It can be very messy to upgrade for a sizeable chunk of developers. Linked libraries, lost compatibility. If the system gets unstable you lose years of installed dependencies. I mean some of the unix apps take literally hours to install, and a faulty upgrade can lose tens of them. You forget how you resolved conflicts, gotten stuff to work.
Why would you figure out how to install something, and then not automate it so you didn't have to do it again? I think if you can't recreate your system in an afternoon with just a backup of your user files, then you're already on borrowed time.
