I would like to comment on this, and I think I can understand everyone.
For developers it is often easier to just focus on SVN and similar.
For users, a simple way to install something is preferred (like an installable .exe)
Personally, in regard to UFO AI, or also wesnoth, I never care about the stable releases.
Stable means boring (for me). I don't have a big problem with bugs, I rather appreciate bugs but keep the "feeling" that things improve, that a game can evolve and similar. This is why I avoid downloading stable releases of Wesnoth or Ufo:AI, but I can understand if users prefer stable versions. (This is just my personal opinion btw)
I love to try out new things! It feels as if your opinion has a tiny impact on game evolution. (And active help is of course even more important than just giving opinion and feedback)
Users will always complain, of course - people love to complain. It is in their nature.
But a project needs to show that it is alive.
The monthly updates are COOL to have, and so are the unstable releases.
Not every complaint is important. But, I think the complaint about two years since last solid release is an important one, and should be addressed in the next... let's say... two or three months.
But again, just my opinion here.