Which is to point out that the war in Iraq has lessened supply, not greatened it and hurt oil prices not helped them. China itself imports roughly 50% of its oil already. It has enough preserves to sustain itself for 6 years at its current rate of consumption. However as their economy grows, so does their consumption and its estimated to continue to grow at a rate of 7.5%/year for the next 20 years. That means after 10 years, their entire reserves would only last them a single year. The United States dependence on oil stems from motor vehicles, which is something that can be adjusted. Regardless in any military conflict you would want to control the supply of oil in order to hamper logicistics and drain their reserves, especially given Chinese reserves would last them a very limited time span.
I'm not agreeing with the policy but its of far greater strategical and military value than economic.