Facebook makes advertising money through user profiling and only from within their site. Google makes advertising money just from the fact that you're using the web. Google is able to do more though profiling, but they have the flexibility and hindsight to do it less intrusively. Remember, Google's properties are more spread out than Facebook's (and AdSense is almost everywhere). So with Google you don't even have to be logged in for them to advertise to you.
