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.
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But again, just my opinion here.