I disagree. The ones that make the front page are often interesting and I use the front page as a filter to keep me from spending too much time on HN while at work (as I would bet a lot of other people do something similar as well).

I know you can treat the front page of the ask section the same way, but now its a filter of a much smaller set which means that "top 30" is not as good a filter (in addition to doubling the number of pages that are on a "front page").

I would think that its best to create disjoint sections only if people usually want to target one section or the other, which I don't think people do here (though if I'm wrong, I would agree with your idea).