The question that springs to my mind is what will Amnesty think of a fund raising venture based on a game killing everything in sight! Doesn't seem to gel with their profile ;-)
They'll never reach 10,000,000 sales so there is no way anyone is going to get the game for a dollar - if they did the business would be bankrupt because they have promised to give 10% if the target is met and if they do I can't really believe that there will be more than 10,000,000 people world wide that would actually want to play the game so they would get few more sales from it.
I know it isn't a fair or obvious comparison but I don't think Portal 2 has hit 10 million yet but has been named as best selling game of the year - and that is across PC, Mac, XBox and PS3, including digital download and retail copies.