I learned to program on PLATO. It was an AMAZING system. In addition to supporting a variety of development environments, their system used a proprietary language called TUTOR. A good bit of networking technology today is derivative of this amazing system. I wasn't rich, although I noted a lot of kids who had access to PLATO tended to be children of CEOs and such. My parents worked at a college that had a grant to have the terminals available. The games on the system were also amazing.
As a programmer, PLATO was a great example of the "cloud"-type systems that will eventually become standard.. what Google is doing and Adobe is now proposing was done in the 70s at Plato, with centrally-hosted apps that routinely are updated automatically. As developers we could put in requests for program features and see them reflected in newer versions of the API. 512x512 resolution, touch sensitive screens, multi-player, real-time games between people all over the world..... in the 70s.
By the way, the original PLATO system has been ported and is running over TCP/IP. If you're willing to donate to the project, they have been known to grant access to people wanting to experience what it was like. See: http://www.cyber1.org/
By the way if anyone has the archive of the PLATO game 0drygulch.. PLEASE contact them... we've been dying to find that code and put it online.