Ah, I see this discussion has been already ongoing! How vain of me not to think someone else would have raised this issue!
So, to step in and offer my two pounds fifty's worth, I can see a need for SOME sub-genres, reading the reponses here. I love SOME metal, but not all. F'r instance I'm a loyal acoylte of Maiden, I like Kamelot (I know you said they weren't metal Jack, but bear with me), Adagio, Sabbath, some Motorhead, Lizzy and so on, but then there are a LOT of bands I would not personally listen to. I may have mentioned somewhere else that I can't hack what are apparently described as "death vocals", (but which to me is just growling), so bands like Opeth, Haggard, Slipknot etc will never grace my Zen. Doesn't mean they're crap, just that I don't like them and have no desire to hear them.
So if I can differentiate MY (as it were) metal from THAT metal, by use of a sub-genre (let's say, Classic Metal --- oh no, it would have to be written Klassik Metal, wouldn't it?)
, then that's not too bad. But reading the list of sub-genres here, and I have to agree with boo-hoo, some of those names are AWFUL ("Drowning in a sea of mourn"? That's not even a sentence --- a sea of mournfulness, maybe.. Sorry I'll shut up before I piss off that band's presumed legion of fans), it does seem overkill.
I mean, can there be THAT many different types of metal? Someone else here said that metal seems to be one of the two only genres that seem to need this, and I wonder why? Is it an elitist thing? Oh, I'm into Viking Doom Proto-Foeutus HyperScare megaspeed Metal --- what are YOU into?
Or is there some other, deeper reason?
The other, linked question I guess is, what MAKES a band metal? Of ANY sub-genre? Is simply playing too loud a qualification? Looking ugly? Professing to worship the devil? Lyrics about death and speed? But not every metal band does this. So how do you categorise a band as heavy metal, BEFORE you even get into sub-sub-subdividing it into one of the exponentially increasing number of sub-genres?