Peer to peer or client server

Reading a little on Ruby over the weekend I was struck by how artificial we have made that boundary between client and servers (Note: I have very limited knowledge of Ruby so excuse an inaccuracies). Ruby has a built in http server as part of the language. This seemed very sensible - most other language environments make http servers/interfaces a different part of the system.

This blurring of the lines between client and server seems to be the right direction. In this I would include AJAX both the client and server can send and receive events the only real difference is who is in control (machine or human) - does there need to any other difference's? It should be all about breaking down the barriers!