I know you're just quoting the standard line, but without "not hacker news!" postings, how do we, as a community, transmit a sense of what is and what isn't? Just let people guess why articles are killed - if they are? Thinking about it a minute, I'd rather have a loose rule along the lines of "not hacker news" comments should be relatively verbose in terms of what is wrong, rather than a simple, dismissive "not hacker news!".
I think the appearance of articles like this is a good indication that this sense of what's appropriate hasn't been transmitted (or at least my sense of it:-). This article is blatant politics/reddit bait, and is certainly not something that would be of more interest to hackers than to the general public.
The NHN comments are well intentioned, but boring reading, and bad for the signal-noise ratio. I think the guidelines are fuzzy enough that reading a debate about every edge case is tiresome. Your NHN is another person's "of interest to hackers" so I'd rather flag and let the mods decide.
I agree on your ideas about feedback, but maybe more elegant and help the community grow is if mods left "why killed" comments on the edge cases, but volunteering other people to do more work is easy, so I try to avoid it on principle :).
If you don't like it, the better approach is to flag it. "Not Hacker News" comments aren't Hacker News either.