Why do different pions have different lifetimes?

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I don't understand why the pi(+) has such a long lifetime compared to the pi(0). Can anyone give me a simple qualitatiive explanation of this?
 
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pi(+) and pi(-) are quark-antiquark pairs, each of which is an up and a down. pi(0) is a quark-antiquark pair consisting of 2 ups or 2 downs. When a matter particle and its anti-matter opposite come together, they anihilate (sp?) each other very rapidly. This explanation is somewhat of an oversimplification, but you can see why the pi(0) has a much shorter lifetime.
 

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