That's an interesting question. It's similar to "What do Linux developers make money, like Ubuntu?" or "How does Sun make money from
Java?"
The answer is: market share. If Android ends up taking Symbian's market share in 3-4 years, then Google's stock is going to benefit because of people confidence in the Google trade mark. Also, in such a case, 30% of all revenue for all paid applications go to them, which would be a lot of money at that time.