[codexon]

a) How are they market specific? Stackexchange tries to target every possible topic that is popular, while Quora targets every possible topic.

b) See above

c) Is there any evidence for this? ChaCha also has comments. The badges seem to be a gimmick to promote addictiveness, the novelty of which seems be gradually wearing off. Does a Google searcher care about the addictiveness of a website, or do they care about finding what they want?

d) The majority of topics are not discussed from relevant links from blogs and tutorial sites. In fact, many of the answers from Stackoverflow are taken from blogs and other websites.

I don't even see the tip of an iceberg.

[Rusky]

a & b) StackOverflow itself is very specific and is probably a better example of having a specific market with pro users.

c) ChaCha may have comments but, like in (b), who participates in them? Knowledgeable members of the field? Definitely not for ChaCha.