In order to see the demo pages you must be running a recent version of Firefox as good old Internet Explorer does not support HTML5 completely yet. Still, as you can see in this demo it is possible to incorporate MusicXML in a fairly clean notation format. The demo site only shows single line notation coupled with guitar tablature but the site for the open source Vexflow API that actually allows the magic to happen shows that it is possible to render more complicated documents as well.
Another point that this new technology brings up is that it is hopefully a sign of things to come that one day MusicXML will take over as the default music notation file format for music writing software of all kinds. Instead of worrying about having to export a composition to MusicXML and losing some of its markings in the process perhaps one day all editors will be able to open, edit, and save MusicXML in a lossless way.