becuase you use a quote to make a direct reference to that post. with no quote people assume you are talking about the subject, as it is in that thread. its understood. the whole thread is a reply to the first thing
however witht the way this site seems to operate, people tend to go off on crazy tangents and it is useful to also paraphrase bits of the original post...i think it would be a valuable asset to the newschoolers online community.
I'm all for it. If you can quote everything else, why not the original post. Especially for longer posts, being able to selectively quote stuff would be awesome.