I think u got a point, but I just think it makes it easier to get idea of what people are talking about when "subgenres". There is a fundamental problem in communicating this kind a stuff in the first place (I mean talking about music) and this just makes it a bit easier. But as u say its all subjective and one has to always consider that, and thats all u have to remember when u r reading reviews or discussions imo. Other wise it would be even more difficult to have a sensible discussions about music which is by concept already a confussiong thing since we are all trying to put words into something that is a wordsless sphere, it all bites itself in the tail really. So even though u r right that u cant really talk about exact bounderies between subgenres and stuff I think the alternative is worse (all imho of course). (All words are by difinition false anyways since its all just subjective labeling of the natural world, and that we have to live with )