Vive la PaaS difference.
SamRay, yes, it's a little blase to refer to many different forms of PaaS. But that's the case. Google App Engine started out as a platform that welcomed and supported the creation of Python applications. Why? Because Google's favorite language at the time was Python. Azure was focused on C# and other .Net tools because it was Microsoft's PaaS. PaaS emerged as opionated cloud development environments: the sponsoring vendor was expressing its opinions about what's valuable to development in a cloud environment. Heroku, Engine Yard, Red Hat's OpenShift, and Cloud Foundry have sought to get away from single vendor opinions and become general purpose environments. But it takes many more graphs to explain the differences, and that's not the purpose of this piece.