Trouble with Genres

People tend to argue that today's country music doesnt sound like the music we called counrty from decades past, and therefore we shouldn't categorize it as country. The same can be said of many other genres of music. If today's counrty music sounded like older counrty music, we would be complaining of its staleness. While i love Johnny Cash, Hank Williams, and Loretta Lynn, if artists today sounded like them, we would tend to call them unoriginal copycats. While i do not like modern counrty music, i accept that it has to evolve from yesterday's country, whether i prefer the direction or not. The same could be argued for all types of music. Instead of lumping it into "country" or "rock," simply break the music into subgenres. Thing is, alot of music is hard to categorize at all. how do you categorize the decemberists?