Actually, Black Sabbath, Iron Maiden, etc....all of the bands from then who influenced metal twenty years ago all the way to today. Guess what...they're STILL metal. AC/DC are not and have never been. They have always been arena rock-style stuff. They were heavy for their time, and I'm sure they have influenced metal bands, but that is not enough to call them metal themselves, in my opinion. Whereas most Black Sabbath songs, for instance, have compositional depth in the form of narrative structures or even just plain old epic/long songs with drawn-out instrumental sections (a big thing in metal and for the development of the instrumental capability prevalent in a lot of extreme metal, as well as the atmosphere of black metal, I would even say), AC/DC never did anything like this. They have always been verse-chorus-verse vanilla rock.
@vihris-gari: So on a gardening forum, if someone made a thread about synthetic plants, it wouldn't be grounds for deletion or closing/locking in the GENERAL GARDENING DISCUSSION section of the site? What?!