We also have a container and compression in Avalon. I would expect that in the future, the export from tools will expose this in addition to the plain XAML file.
If you are just moving it to another tool or want to do some XML processing, a flat file may be better. If you want to store or send the information to someone else, using the container and compression is the best option.
Any application or content built with Avalon by default looks like other Windows applications (matching the themes on XP or Longhorn).
However, what will applications look like 3, 5, 10 years from now? The user experience
will not remain static. Avalon provides the platform that will carry applications and content into the future, removing the roadblocks from today's platform.
Avalon provides an unique platform, enabling folks with great ideas (at Microsoft or anywhere else) to experiment, innovate, and develop new interaction paradigms.
We do desire and expect consistency in user interaction, but we expect that this consistency will evolve over time, and we want to ensure that we provide in Avalon the functionality that enables and fosters this evolution.