Who says there's nothing on the type but those properties?

How do you know there aren't private members that hold the geocode?

How do you know that the DistanceFrom() operator can't communicate with a map server?

The key here is encapsulation. You don't know -- and as an end user, you shouldn't have to know -- how it works. It just works. As a DBA or developer, you know the details. But you don't need to expose them to the world.