Why Aren't China in G8?

China's shadow hangs over G8 says Yahoo News. Of course it does, given China's increasing importance. The question is, why aren't China included while much smaller economies like Russia and Canada is? Like it or not, China is one of the most important economies of the world and is becoming more important all the time, and if the intention is to gather the world's most influential economic powers it makes no sense to exclude China, while including Russia and Canada.