I once tried to write something on this topic, about the differences between American and EU metal, why US bands are more about politics than their EU counterparts. but there were some servers problems, so I couldn't post. I post it now, (even though discussion seem to change direction)
Since 80's, except Clinton period, USA is governed by republicans, conservatists. Aggressive world politics, not caring enough for social peace (i.e. New Orleans after Katerina storm) And inevitably, angry crowds start to appear. it's not a coincidence that politically driven bands turned their angst to their own lives and family problems during Clinton era, a democrat government with more social sensitivity and relatively softer world politics (megadeth comes to mind, and the rise of grunge). And with Bush II, political messages are appearing again on music (even Green Day...) And the consumerism doesn't help people to be happy, as it makes people forget how to be happy with what they own, and makes them envy things they don't own, to get more and more.
let's look at Europe, mostly Uk and Scandinavia (where metal is strong). Political music was not a US-only phenomenon. Think of late 70's-early 80's. t Punk, Sex Pistols dominated UK scene. Iron Maiden itself refers to Margeret Tatcher. Then, when the cold war started to end, political music started to fade too. As I said before, scandinavians live more in peace with nature, protecting human rights, providing more and more social services. people aren't so rich, but they live in comfort.
you can't expect those people to complain about their governments, their lives... They complain about religion and other oppressive stuff though.
"bleeding reality" as a US poster said in this topic... (why the word "bleed" btw? even the word is violent, morbid). Not all reality bleed. Think about it.
PS: And now, in 2006, where UK backs USA without question, Iron Maiden issues AMOLAD, an anti-war metal album.