That's Joel's version of link bait headline. It works nothing like a wiki. But of course, you already know that if you've used Stack Overflow. But, tomato, tomato.
Microsoft built several of these Q&A systems that are "easily achievable by any competent group of engineers". They never really took off until they got Stack Overflow Enterprise. So, I guess it isn't really that easy.
Note: I'm a former Microsoft PM and currently a Stack Overflow PM. My POV comes with bias.