Google is indeed smart. They have released a Google Maps API that allows you to embed Google maps in any web page.

Notice the bold point below.

“The Maps API is a free beta service, available for any web site that is free to consumers. Google retains the right to put advertising on the map in the future. Please see the terms of use for more information.”

Google gets the benefit of an army of web developers creating value added applications on top of Google maps, like Busmonster, which collectively become a distributed canvas for Google’s advertisements.