Canonical originally planned to replace the aging X with another displayserver called Wayland, but the developers apparently couldn't bend the compositing-friendly protocol to their cross-device whims.
And Ubuntu has been using the standard-issue displayserver to push its GUI to monitors across the globe since its color scheme was more sludge than slick.
It can't delete mail from the inbound server, either, but it can display Word and Excel attachments with the help of cut-down versions of the programs included in the package.
The Sun Ray appliance effectively becomes the end node of the network, and its function is to display pixels on the screen, capture keyboard and mouse clicks, and send them back to the server.