Not every metal band uses it actually.
Check out all the 70's 80's metal bands.
Also, if you want some modern bands, I reccomend
Nightwish http://uk.youtube.com/watch?v=6UztEfwHt14
Airbourne (if you like AC/DC) http://uk.youtube.com/watch?v=uANVBPVaf-g
Hammerfall http://uk.youtube.com/watch?v=Fi66fs7xRoc (Rand, if you like Dragonforce, you'll like these guys too)
Skyclad (who were the original folk metal band) http://uk.youtube.com/watch?v=nlo7F1Zd-x0
Iced Earth http://uk.youtube.com/watch?v=cr--nPBEEFI
And there's loads more.
As Bruce Dickinson once said "Some people take comfort is fluffy bunnies and flowers... Some... Take comfort in drawing Swords and dead people all over their school books. And then a band comes along and sings about that, and you're like YEAH! That's how I feel... NOW!!!"
... Heh... Bunnies have fluffy tails...
"Growling" As it's called is a style of singing, Most people who growl well, can also sing well.You mean the "I can't sing, but if I yell loud enough it won't matter" voice?
That bugs me too. Still, Geek Rock.
But saying that, growling is style singing, much like opera is a style of singing.
And you assume that it's easy, but it's actually very difficult and takes a lot of practice.