Yes, it is. services might actually provide pages other than admin pages - I think I unintentionally misled you in this regard. The workflow package, for instance, has a user-visible pageset.
So the real definition of "service" vs. "application" is that the person
who wrote it decided to call it a service instead of an application...one hopes that the definition you've provided is more-or-less true for most of the packages, but don't depend on it!
