Exactly, and if you include a little Powered by AWS CloudFront i am pretty sure they could drive down the price a lot. Or, they could start talking to Fastly, I am pretty sure they can work out a much better deal while being faster.

Amazon doing anything for free for the open source community would seriously shock me.

They do spend a lot of time courting ruby/rails devs, though, so being able to say rubygems is hosted on AWS might be worth throwing them a significant discount.