Yeah, agreed, the other half of things that I didn't mention is that when I do find a good stand-alone community around a technology, that tends to be my go-to place. Especially for free ranging conceptual discussions.
What I see more of these days is a Google Group, or mailing list, or forum with a lot of core users discussing things, planning the future, debating, etc., and then a lot of reference back to Stack Overflow for particular questions that get asked a lot.
And that's really the core purpose of Stack Overflow. When it comes to writing documentation, the area that tends to have the most potential but the least realization of said potential is the FAQ. FAQs provide another dimension to documentation because they address the, "Well, given that I read this documentation, I still don't get X" scenario. No matter how well written the documentation is, there will be things that are not answerable, because software is so multidimensional. Usually the way a FAQ works out is that the person writing the documentation remembers a bunch of questions that were asked and answers them in place. Hopefully people come in later and fill in more answers based on questions that come in later. In the end it languishes. People have tried to address this via forums, wikis, and mailing lists, but in the end forums are a good place for narrative discussion, wikis are a good place for writing documentation period, but both are poor for FAQ because of their built in time decay, lack of voting, etc.
In that sense, Stack Overflow is a FAQ engine is appropriately geared toward explaining particular answers to particular questions.
That said, Stack Overflow became more than that after its community exploded, and I share in the annoyance when some of the more interesting free-ranging questions get shut down because they're open ended. I am not wholly on the side of FAQ-type lockdown.