The data is there - it is just not shown at that particular zoom. This is handled by the Map File that determines how to render items at given zoom levels.
Many consumer-oriented applications degrade the underlying map data to make the consumer app faster. This also allows them to show more detail at higher levels. This is good for a consumer app, but not appropriate for an enterprise application interfacing with real-world items.
Telogis is currently in Alpha with a tool that allows the application provider to customize the map files. This allows the developer to go up in quality to provide richer maps in an ASP or client application. This same tool will allow you to go down in detail - in case you want to send navigation tools to a Blackberry or a Nextel phone.
Below is a consumer application:
This is the same region in GeoBase:
