An application to OnlineCommunities is that some people are more likely to post on something like a wiki than on a forum like SlashDot. On a large static discussion board, no one has time to read most of the comments, and most individual comments don't feel like they are getting much attention (although it is thought that typically at least a large handful of people read any given comment). Why spend time composing a long, thoughful post when the chances are small that very many people will see it?
On a wiki, on the other hand, pages are constantly refactored to keep them within a manageable size. You have the assurance that even if your comment doesn't persist, if your comment is considered valuable it will probably be refactored into longer-lasting text. In addition, the WikiNow allows contributions to be valuable for a much longer amount of time than they would typically be if posted on a time-oriented WebLog.
The WikiNow also means that you don't have to confine yourself to the topics-of-the-day in RecentChanges. If your idea is topical to the wiki then your contribution will persist in the WikiNow, even if people don't read it today. In other forums you often have to "save up" your ideas until the proper time. This is not to say that your ideas won't be more persuasive on a wiki if uttered when others are listening; just that they won't be useless.
It is important to note that in a wiki although YouWillBeHeard, you will also be refactored. For example, your comment was read and deleted, you have still been heard in this sense. YouWillBeHeard simply says that whatever is useful in your contribution will (probably) be used. If nothing was useful, nothing will be used. This is still much more comforting than a forum like SlashDot. In such places any post will more than likely be seen by only a few people even if it is well-written and useful.
YouWillBeHeard is one reason that PostNow makes more sense on wikis than elsewhere; however, caveat scriptor: your writing will be deleted if it's poor or meaningless. If you want to be listened to, write something worth listening to.