App URI should be RECOMMENDED but not required.

[marcoscaceres]

From the mailing list:

It should not be a requirement that packaged apps run off the app: URI scheme. The runtime spec should RECOMMEND it. That should address Giri's concerns and give more freedom of choice if implementers want to use something else (e.g., a local http server per application). Again, all that matters is that the results are predictable and interoperable, not that app:// is used.