I think the common view of looking at great answers like this and thinking, "wouldn't SO be great if discussion was allowed" is similar to looking at a great work of graffiti art and thinking, "wouldn't be great if every kid with a spray can could paint all over the city".
These answers are outliers, special snowflakes among a sea of crud that fills the programming PHPBB boards out there. Joel and Jeff were trying to solve the bigger problem - having a decent Q&A system -, and that can only be done by looking at the average case and not the exceptions.
> "wouldn't be great if every kid with a spray can could paint all over the city".
The thing is that, unlike in other places, people can upvote/downvote stuff on SO/SE sites, and just like crappy questions and answers are quickly buried by the community the same could happen to subpar discussions, so I don't really think that's a valid excuse.
These answers are outliers, special snowflakes among a sea of crud that fills the programming PHPBB boards out there. Joel and Jeff were trying to solve the bigger problem - having a decent Q&A system -, and that can only be done by looking at the average case and not the exceptions.