I agree, while this list is very good - and I wholeheartedly thank you for putting it together for us - it's very much biased towards the U.S. Of course, if the U.S. so much as sneezes, the rest of the world reaches for their handkerchiefs, thanks to the globalisation.
However, very few pictures indeed have had an actual impact on politics and thus changed the world. Yes, the exploding 'Challenger' Photo is missing, but inhowfar has it changed the world? We still send people into space. Yes, the 'tankman' photo is missing, but what has changed in China since then? We choose to look the other way and try to get into business with the regime.
Yes, the picture of that Afghan girl with the piercing green eyes is missing, but what did it change? Are there no more refugees in Afghanistan?

There are so many excellent photos depicting the horrors of war (any war, for that matter). Has it kept us from going to war? We have seen bodies on the field of Gettysburg, bodies piled high in Auschwitz, bodies draged through the ruins of Mogadishu and bodies from virtually every corner of the earth. Has it kept us from killing? Now we have seen Saddam hang for his deeds, but will it keep us from shaking hands and making business with the next devil? I doubt it.

These pictures are like matches. They have the potential to ignite a flame, but more often than not we choose to extinguish it. It's up to every one of us to change the world.