I think that really depends on how the forum is structured. Usenet suffers from having a horrible signal-to-noise ratio, and while mailing lists aren't bad, they nominally lack googlability and any sort of ranking system.

So, I think the problem isn't that web forums are bad, merely that the interface for using them isn't as good as a newsreader. Might be a good opportunity...

I think that the fact that Web forums don't require readers is what contributes to their popularity. They have a low learning curve.

That said, the fact that they tend to have a government of sorts, can be a big advantage. A forum can potentially do away with trolls and encourage intelligent conversation in a way the Usenet cannot.