You don't seem to know many forums, because that's exactly not how a forum works. A thread is no collection of semi-related posts that can be viewed in any order, or something like that, a thread is a conversation between people where each sentence has a fixed point in time, and won't make sense elsewhere.
And yes, if many people are in a thread, there might be many quotes - and no, this doesn't bother anyone in the forums I frequent
The beginnings of Stackoverflow, where the vision what a tiny bit different (a "library" of google-able answers, not a personal support site for coding problems) was when many good programmers came and made good content. The fundings (risk capital etc.) and marketing of the company behind it helped much too.
Then the policy changed, and the policing started to get annonying, and many people left again. The ones that stayed are either the ones that post masses of "easy" answers to get masses of reputation points, or the people that are too stupid to find something else to get help. (No racism intended, but ) nowadays most askers seem to be from India, where a unreasonable government forces them to use 30 year old tools in programming education, and they noticed that on SO at least someone remembers them.
Summary, a lot of indians, a lot of help/reputation vampires, a lot of trolls and spammers, and a lot of people without common sense acting as police. Some good programmers with a thick skin too. Nonetheless, SO is just numbers, not quality, anymore.
Most smaller network parts (ie. sites other than SO, SU and SV) don't do well at all. Some got some popularity because there are not many forums in that area, others just never lifted up from the floor.
...that's not a fault of the Q/A format. But the QA format alone won't get you many users (and it won't get you a poisoned community either).
