Excellent points, buz. How many times have we seen posters get accused - especially in heated debates, or where you're down to the minutiae level - of ignoring or skipping points, or not reading the post, or taking bits out of context in a reply, etc, when they DON'T address each line? I think it's a structural problem of this type of debate forum. I often feel constrained to say
something about each statement made simply to avoid having to go back later and explain in a subsequent post that I ignored it because it was irrelevant - and then be accused of glossing over the utterly insignificant statement that all of a sudden becomes crucial in the mind of the poster I'm replying to. After all (the thought goes), if I didn't address it, obviously I couldn't, etc ad nauseum. Borger was notorious for it, and there are several current posters who operate in a similar vein (although usually more logically than Borger did).
One possible solution (which I've occasionally used) is to use the quote or qs function with the first and last few words of the section to which you're replying only, separated by ellipses. That makes it a bit slower to post, and makes it a bit harder to follow for readers, but does cut down on space - which seems to be CrankyMoose's main objection. Another problem with this idea is that many people simply don't make paragraphs well - they contain a number of different points, all of which need to be addressed with separate replies. Tis a puzzlement.