If one creates a subsite, say newsite, and mounts packages foo, bar, and baz at that subsite, then the following uris will be valid:
while the uri, www.site.dom/newsite/zot will not be. No surprise so far.
Now, create the dir /www/newsite and edit therein the file zot.adp, and voila, www.site.dom/newsite/zot is no longer 404.
What this all means is that uris reference files until a uri pattern matches something stored in the database. Then the magic works.
I'm still of the opinion that creating a subsite should make the appropriate dir in /www. And that removing it should optionally remove the dir. But I can script around this.
Now, if I can figure out how to move /www out of the oacs dist filestruct, I'm golden.