> Amazon has not really made a serious effort to encroach on Heroku's profits
Amazon hasn't, but there are a reasonable number of simple PaaS competitors these days:
Microsoft's Azure (http://www.windowsazure.com/en-us/pricing/details/web-sites/): ASP.NET, PHP, Node.js, Python
Red Hat's OpenShift (https://www.openshift.com/): Java, Ruby, PHP, Node.js, Python and Perl
Nodejitsu (https://www.nodejitsu.com/): Node.js