i'm not sure why people get so fussed by the genre terminology and semantic distinctions. quite a few people (nearly all Americans) have responded to the concept of "postpunk" as if it's an affront -- and as if hadn't actually been in widespread use since 1979! i mean i've trawled the era's music press, it's used quite often that early and by the time i was doing my own fanzine Monitor circa 1984 it was an established term for that era, and had these associations with a particular kind of music. so it's kind of a futile battle to resist what is an established social fact. when enough people use a certain word to signifiy a certain entity, there's not much that can be done about it
but mainly i'm not really sure what is at stake in the proposals some had made to refold postpunk into "punk" -- what would actually be gained except to make punk itself meaninglessly expansive? A historical sense of punk itself is best served -- and I think is actually more flattering to punk -- by the idea of it as a short sharp shock. That a lot of people got stuck on that particular moment (Oi! etc) is not necessarily to the detraction of the prime punk moment itself
like all cultural fields :postpunk" is is fuzzy at the edges, fuzzy at the start, and fuzzy at the end (which doesn't end, in so far as the bands themselves mostly carry on after 1984, johnny-come-lately bands doing postpunk-y type things after 1984, and then you have later bands who refer to or reactivate ideas from that era (radiohead, nine inch nails, whoever), so postpunk is still with us to an extent). but for all that fuzziness the area/approach/attitude has enough coherence that people can use the term postpunk and other people know what it's referring to
i don't really see postpunk as a slight to punk, it refers above all to the idea of the next stage from punk; not necessarily the refutation or cancelling of punk, but an attempt to move on from it. But because people disagreed about what "the next stage" would be, and indeed disagreed about what the really important element of punk was, you got a panoply of directions, an ever-widening delta. in that sense, you might say that postpunk is the actualization of the internal contradictions of punk, or the releasing of the dissensus that for a year or so was contained within the pseudo-consensus of the word "punk",
the "post" in postpunk is similar to the post in postmodernism -- the latter isn't the cancelling of modernism, but a kind of relaxing off its strictures, a kind of selective betrayal of its tenets, an attempt to sidestep certain blocked paths and dead ends. The original impetus of modernism subsisted in postmodernism in the very demand to keep on innovating; postmodernism was not about a simple return to tradition or classicism; it was a response to the becoming-tradition, becoming-canonical, becoming-institutionalised of modernism after WW2.
A similar kind of complex set of reactions and relationships with the precursor informs postpunk activity; there is a simultaneous move of keeping faith and breaking faith. From this point of view staying true to punk as a form (Oi!) or indeed in terms of a narrow idea of its content (Oi!, anarcho-Crass) would be to betray its spirit (change).