>I don't see how they can claim that their own Java APIs can be copyrighted, and then defending their copying of Amazon's API on the grounds that an SDK using it is open source. I would think they could just look at the documentation, and skip the SDK altogether. :)

They took an open source piece of software (the SDK) and made a derivative work (the backend the SDK uses). That indeed is copying and is essentially identical to what Google did. But there's no copyright violation here because Amazon explicitly granted everyone the right to do that by releasing the SDK under the Apache license.