trust and brand:
best on web for my line of work (webmaster ;). when i have a coding problem i always come here first. there are members in certain areas who are the top guys on the web in their respective fields - and freely give this info.
when i first joined this was the only place to get such info. that is no longer the case. i think blogs, and particularly those from people i trust/follow, also provoke inspiring discussion and provide interesting solutions to many problems.
i don't believe there is a solution to this; you can't monopolize good content. but you can expand the offering (as has been discussed many times in this feedback forum) to keep people coming back.