These guys could do at least 10 minutes of research before writing an article. The AWS APIs are already 'open source', you're allowed to write free-software tools that use them. They're out in the open, with no NDA or anything attached. Eucalyptus also exists, which is a pretty darn good reimplementation of EC2. The only real impediment to an 'open' (you meant free, right?) cloud is that you can't use ec2-tools with it unless you want to fight off a pack of female Amazon warrior-lawyers. I hear their punches can leave a mark.
I'm too lazy to send them an e-mail, and the Slashdot comments are already calling 'em out anyway.