A forum is topical, so narrow interest posts are channeled into topic areas. In a forum you might have a topic "Co-Founders Wanted" but only people interested in being/finding co-founders at a given time would read and post in that topic. If Hacker news was mainly narrow-interest postings (ever seen this bug?, co-founder wanted) the signal to noise ratio would degrade.
A Hacker News Forum would be great because 1-this community is great and 2-I could browse topics I'm interested in at the point in time they're of interest to me.
(Most of my concerns are NOT technical. I can go to Webmonkey or Barnes & Noble for that. I'm more interested in how others like myself handle similar situations, technical or business. So far, I haven't found anyplace better, but if anyone does, I'm all ears.)