As is said so many times in what we do, if it's that simple why don't you hire a few hackers for a few weeks, build it, and then compete with them? SE has a very polished platform, unbeatable service (presumably, since it's backed by Fog Creek), and a great sample implementation that you can look at to see exactly how much information is exchanged/value is added to your network. They've also got Joel and Jeff, two very prominent voices in the space.
As for the price point, I don't think they're going for small five-person shops. My guess would be that they've got two markets targeted:
* The internal company knowledge base. In this, they'd be taking a run at a small part of Confluence, and the price point doesn't really matter. If you're in this space, $3K/month is nothing if it makes a production team more efficient.
* Support/community building for a third-party product. Most company support forums are, after all, basically a way for people to ask questions to fellow users/administrators. So why not optimize on a system that's designed specifically around asking and answering questions, as opposed to a form that's meant for discussions? What immediately comes to mind, for example, is BlackBerry third-party software development. It's not bad once you've got the hang of it, but it has a lot of tricky parts to get going and optimize. So RIM would get an SE site going and say "we encourage everyone to ask their questions here, and we'll have a team of a few community relations people hang out here to do what they can." Gives the community a focal point, and in a way that promotes getting things done, as opposed to complaining. Think of it like a version of GetSatisfaction for technical support.