So the Calendar app is using the Gdata api which is an extenal api that seems to be included in android as a platform jar something that is not part of the official api. So a way to ship around that is to provide the Gdata API with each app and bundle the jar with it. There is currently no way to distribute a jar with an apk and have it only once in the system. A way that could overcome this is by making the api available via a service or content provider. Interesting idea indeed.
Oh I also posted a new thread on android-platform about the gdata api