Mainstream, easily accessible music is always about what sells and whats marketable, not whats good. And I think, just like the gaming market, there's always more casual gamer than people who take gaming seriously. So there's the causal listener majority who likes catchy songs, who likes following whatever trends thats being overplayed and overhyped on the radio and TV and teh net, music to them is a product more akin to a piece of fashion item than art. Then there's all you music franatics, who go outta your way to dig up some obscure musician/band in the internet from another country, talk about the music industry, and post up threads like this one here
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world issues do have an impact on music, but I don't think it'll be as direct as making 00s releases "angstier". On the contrast, I think people would want more cheerful music; the media, afterall, is mostly for entertainment. An example of this I reckon is the disband of Rage Against the Machine; I've always suspected their break up was related to 911, and my suspiscion is kinda confirmed when they regrouped this year, with the Iraq war turning sour, US election pending, climate change treaties back on the table etc.