Google, in my experience, is a place where smart people go to retire. I have many brilliant friends who work there, but all of them have essentially stopped producing interesting work since the day they started. They all seem happy and comfortable, but not ambitious.
I'm sure the pay is great, but it's not a place for smart people who are interested in doing something. I've followed Francois (and had the chance to correspond with him a bit) for many years now, and I wouldn't be surprised if the desire to create something became more important than the comfort of Google.