Perhaps - and I don't se the benefit of all decisions, like pushing system admin and database admin questions to separate sites. But I do think the overall perceived value of the site would decrease if general discussions, joke threads and unfocused flamewars were allowed to run wild. The basic premise of SO is that "it answers your question", and I believe it does this extremely well. I remember a time before SO.
But that is a decision for the owner of the site - Joel Spolsky I guess? Don't blame the mods for keeping the site at the intended focus.
There are also frequently users complaining about HN not allowing joke-threads. Clearly those users are not served well by HN and have a bad experience here - but would it improve the site to cater to them? Are all customers always right?