The community isn't a given. Some of the stack exchanges that allow more open ended questions are somewhat useless. I'm thinking of the stats one in particular[1]: you get a ton of questions where it is clear that the questioner will be unable to determine which answer (if any) is correct. Here's a random example I found after 3 seconds of looking:
http://stats.stackexchange.com/questions/32007/which-statist...
Fairly open ended, possibly answerable, but the OP will have no fucking idea if an answer is good or bad. (Apologies if the OP reads Hacker News).
Now, the fact that the stats stack exchange also encourages students to ask questions about homework introduces the similar problems, so I can't be sure that the open-ended nature of these questions is the main cause of the site's suckiness, but I'm pretty sure it contributes. And I don't want to participate in that forum even though I waste a shit-ton of time online on places like HN and prefer stats to startups.
[1] http://stats.stackexchange.com
