It seems to me that American black metal is usually the more nihilistic kind, e.g. evoking the beliefs and image of Satanic/pagan/neo-nazi black metal without actually believing in those things. I remember reading an interview with Josh Gossard and he talked about how his lyrics would change periodically (I think "kill your family" and "kill the jews" were examples he used) without regard to what they actually meant. Whereas Nordic black metal (these are generalizations, the philosophies certainly crisscross at times) which is often of the truly Satanic/pagan/neo-nazi brand, seems to be a bit more fanatic and socially-unaware than nihilistic. Don't really like the image of either, as communication is an important part of how I appreciate music.
But, of course, as Jonas said, there is definitely plenty of black metal that focuses on other things, and I've found bands of that type that I like. In fact, most of the bands I've found so far that I like, while they may not be true black metal, are usually under the black metal tag here. I also like a lot of the avant-garde black metal, namely Kayo Dot, and would trust Toby Driver to take care of my granddad anytime.
