i should also point out that this really stems from something i read not too long on this board regarding Hardcore. Someone said something along the lines of "talking about the latest hardcore album is the equivilent of talking about the latest doo wop album".
What a good thread and fair question. I was blogging just today about how I don't think a lot of people actually like "rock," so zeroing in on punk is a bit less unwieldy. In the early 90s, I remember feeling over-saturated with Dinosaur, SY and Du ripoffs and wondering, "where are the bands that sound like Wire or Gang of Four"? Careful what you wish for, huh? By the 2000s it was all post-punk and post-rock as earlier rocking fuck-punk from SST waned. Now we're in a moment, which still feels great, I think, in which Killed By Death has eclipsed Nuggets as the Bible (or Anthology of American Folk Music) for 48 states' worth of gnarly post-GG bubble-psych.
In other words, I think the resilience of "punk" as a rallying genre-bugle can best be explained by the fact that punk has been subject to major changes in form and content. Is that radical aesthetics or flexible marketing tactics? I dunno. Over time it's not as one-dimensional as civilians suppose, although at any given moment I believe it tends towards the monochromatic. I worry about that now, but there are always outliers, right?
Also, there's always the historical re-enactors and the "punk's not dead!!!" industry. Chances are our favorite contempo-punks - mine are Cola Freaks and GG King, let's say - don't attract the yobs or the bucks that this first tendency does. As much a hoax as the POW-MIA "you are not forgotten" lie, the assertion that punk's dead is hardly as relevant as the one about God being a shitty worm-corpse. Still, people defend, I dunno, The Ramones and Sham 69 kind of like tea party caucasians defend themselves like they were in a targeted minority.
Anyway I'll stop now. We allow the meaning of punk to change in part so we can celebrate its resilience and continuity with everything. It's a fantasy that great records ride in on every day.