To say that Google backing out of China wouldn't affect china is clearly a lie.
If nothing else, it would certainly mean a lot to America. There have been many cases of smaller companies boycotting governments to far greater effect. IMHO, Yahoo, Microsoft, and Google could work together on this, and pull out before the Olympics, if they wanted. Totalitarian governments cannot stand being disrespected, as that is the only source of their power. Whereas in a democratic-republic like America, we don't respect our gov't much at all, and it is the most powerful gov't on Earth.
The key here is showing the world how legitimate we think China's doublespeak is on Tieneman Square and every other issue of note. Their press is full of lies, and now our search engines only return those lies. That's the definition of propping them up. No wonder they don't use America's search engines - they return nothing true or useful at all, and Wikipedia is mostly blocked.