Google's Flyover of Sydney

There are news coming from Slashdot, that Google is about to flyover Sydney to update its google earth image database.
News are that a number of startups are preparing huge signs hoping they will be pictured and then seen from the popular software.
What are Google's real motives with this anouncement?
Well, jumping to the Google-wants-to-rule-the-earth bandwagon, it seems quite evident that the webpages are simply not enough for Google, I believe that they are exploring yet another way of advertising, call it Google Earth AdSense ;)