Good question, I played the Devil's Advocate inside my mind. Here is what I get as return / output: All the traditional elements of marketing are different:

a) Is the target market specific?

Yes for q. & s., no for c.c.

b) Is the target market pro. / high-end users with high sense of fidelity to the topic / site / brand or casual consumers?

Yes for q. & s., no for c.c.

c) Does the target audience return to said sites regularly, participate in a community (with hierarchies, badges, comments and replies etc..)?

Yes for q. & s., no for c.c.

d) Do the specific topics discussed get relevant links from blogs, tuts sites etc.. from similiar fields

Yes for q. & s., no for c.c.

This is simply the tip of the iceberg.