Clothes are trends that always overshadow the music. As Testament Legions said, it isn't mandatory and most of the people that do it, just want to fit in with their fellow metal-heads (i'm not saying all of them) I know people that like the metal look, but certainly there're lots of people that just do it to ''fit in''. Most of the time I don't look like a metal-head. I have short spiked hair and most of the time I wear baggy pants or jeans and shirts (although I do have jackets, jeans and black shirts and I use them pretty often)
Here's a question for ya...what exactly IS normal?? HMMMM this could take a while...think I'll get out some of my psychology books and study up... This would be a good thesis study. I could go to concerts and study the behavior and look of all the people at the show and try to come up with a reason why they look and act the way they do. How different types of music influences different behavioral patterns...this could take quite some time and force me to see many many live shows..ahhh the
As for your question, if you ask me there's no ''real'' normal. It's all subjective and up to the person, the people that are ''normal'' are the ones that follow the trends and are always wearing ''what's cool'' and acting in the ''cool'' way. People differ in opinions, but there's no real normal standard.
If you saw me (sometimes) you wouldn't even think that I listened to metal and the funny thing is that my most loved genres are the extreme metal genres (Death, brutal death, black and some grindcore).
I have a friend (wich listens metal too) and she looks pretty gothic. She wears makeup, skull rings (also a ring on her tongue) and most of the time she wears black clothes and she doesn't even listen to bands as extreme as the bands I listen to (Slayer, Metallica, Soilwork, Pantera, Marilyn Manson don't ask me why!) she listens to lots of other bands too, but that sums it up. Now what bands I listen to?
Nile, Metallica, Darkane, Soilwork, The Berzerker, Death, Obituary, Pestilence, Decapitated, Testament, NP... bah you get the point