Update via Mark Pond for Summer '16:
Automatically Get Geocodes for Addresses (Generally Available)
you can set up and activate the geocode clean rules for your org. Then, geocodes are added for addresses on existing and new accounts, contacts, and leads.
No, they aren't populated automatically when the other address fields are populated. You would need to use a third party service to translate the street address into Geolocation coordinates.
The Google Map control will be doing location lookup for you based on the street address.
You could potentially use the Google Geocoding API to do the conversion and then set the BillingLatitude and BillingLongitude fields. See https://developers.google.com/maps/documentation/geocoding/
I've also had several clients use https://webview.webservices.nl/documentation/files/service_geolocation-php.html
In Geolocation Field Types in Salesforce1 Platform the following appears:
Geolocation fields are useful only once they are geocoded (populated with latitude and longitude data). Address fields can be geocoded using services from Google, Nokia, ESRI, and other sources. However, Salesforce will be rolling out a geocoding service to our customers in the future. (Naturally, Safe Harbor applies.)
Maybe ask your account executive if you can get on a pilot program for geocoding (assuming such a thing exists).