Saying that metal is part of pop culture is casting a wide net for pop culture, since Billboard (www.billboard.com) somehow has a Bluegrass chart and Regional Mexical Songs chart, but no Metal chart.
Aside: if metal is listed on the rock chart, can someone please explain to me why Hey Ho by the Lumineers is #1? Particularly when Some Nights by fun is #2? I think Billboard is getting loose with the language. Or, perhaps, my prescriptivist bent is showing again.