That's the same problem that TV and radio "news" has had for a long time. I don't think the problem has to do with the structure of the web. I think the problem has to do with human beings. And given that this keeps repeating itself, I wouldn't call it a "problem," more just "reality." I agree it sucks though, but presumably the low cost of spreading information on the web will allow niche information sources to flourish. HN itself is an example of getting closer to that.