IMHO, quoting in news and e-mail in general is overused because the available options are all or nothing, and people who don't think of bandwidth ("well sonny, back in the early 80's before you were born I read news with a 300bps dialup...") their readers' time can't be bothered to properly edit. As someone already noted, the threading here is good enough that it is unusual that you even need quoting as context is easy for the reader to find.

If I want to quote beyond the replied-to node, I simply open another browser, cut, paste, add a couple of tags and I'm done. While this is easy, it is some effort and makes me think twice about the usefulness of the quote - I think the existing situation is already optimal.