|Humans are dumb.|
Designing and scripting effective particle systems is a challenge for the designer, especially when it comes to realistic "next-gen" destruction. Explosions involve some very specific processes, so it helps to understand a little about what exactly is going on when things blow up.
CGSociety is hosting an excellent article by Keiron Helsdon on the anatomy of explosions, everything from a firecracker to a H-Bomb is described in detail and accompanied by a bunch of great reference images. Check it out.