Wayland is essentially to effort to move responsibilities to different layers. Some things are pushed down to the kernel (memory management, command scheduling, mode setting) or similar infrastructure (OpenGL, udev). Some things are pushed upwards to the clients (font rendering, window decorations, vector drawing, remote access). This means Wayland has much less to do compared to X.org and that is a good thing, because it removes code duplication and unecessary complexity.

http://wayland.freedesktop.org/faq.html