I know you are joking, but the idea is that different levels of service are given by different people, and they may be layered one on top of another. I believe the term used these days is IaaS, Infrastructure as a Service. Amazon EC2 would be IaaS. Heroku or DotCloud would be PaaS. A PaaS company can have their infrastructure provided by an IaaS company.

It's Turtles as a Service all the way down.

Many parts of Heroku are actually self-hosted: https://thestrangeloop.com/sessions/running-heroku-on-heroku