Far as I can tell, Google is actually trying to move away from the 'we sell adverts' business model currently. In the case of Android, they don't give away their gmail/market/maps, but charge a fee for them. With the purchase of Motorola, it hints that Google will be selling hardware in future. Google's push into driverless cars will also be in the form of a percentage of car cost (apparently). It looks like Google Glass will be a sold product and not sponsored by adverts as well.

So I'm guessing Google understands the problem here as well as anybody.