I think your comparison with Joomla is a little unfair, they have an entire foundation backing them (OpenSourceMatters), Tiki does not to the best of my knowledge.
It's a bit like saying why does K-Meleon web browser suck compared to Firefox. They are completely different in structure and organization, yet they are both open source (and Firefox again has a massive organization backing it). I could reel off dozens of examples, Puppy Linux versus Ubuntu is another off of the top of my head.
It seems like your expectations of open source software are very lofty and focused only at the very narrow end of the spectrum. By your definition single-user (or very small) open source projects should just simply not exist unless the person/s producing them is dedicated to the project for the vast majority of his/her time (ignoring the fact that he/she somehow has to make a living). In all honesty, it seems like you want the open source price tag with the commercial level of support and service. That doesn't seem very reasonable, no one here is paid that I'm aware of.
I utterly disagree with your notion of gift-giving. I never receive a gift with the expectation that the giver somehow owes me. If they were nice enough to give me a gift in the first place then they certainly don't owe me diddly squat. They chose to give me a gift and I chose to receive it. If I don't like/want it, I simply stop using it or pass it on to someone that can make use of it. I think in reality your gift-giving analogy is not really appropriate here. Yes, it's nice that some people are willing to work on software for free and make it available for the general public to use, but they are not knocking on your door saying here enovikoff, our gift to you (and btw you WILL use it or else).
To get back on track, nobody disagrees with you in principle (I don't think), of course we'd all like perfect documentation and perfect code that runs flawlessly, but that isn't the nature of open source. It isn't even the nature of commercial software. Windows is not without bugs and flaws, so why should your expectation be any higher of a project that runs without any (or little) notion of financial compensation to its developers?
EDIT: BTW, I haven't written a line of code for this project. I have however updated some of the documentation when I found it to be lacking, in the hopes that someone else wouldn't have to suffer the same pains I did.