Heroku uses AWS for its infrastructure, but offers Ruby and node.js hosting, so Salesforce and AWS are not directly competing yet. Still, there could be some interesting sparks in this space in the future. How long before Amazon offers Elastic Beanstalk for Rails? Even sooner, we will probably see Rails instances running on Elastic Beanstalk via JRuby.
For now, Elastic Beanstalk is Java only. As a startup founder, this now provides you with another alternative to GAE and Heroku/Salesforce for your self-scaling PaaS needs.