Dan Frommer:
In a word: Ads.
This past quarter, Google generated $9.7 billion of total gross revenue. […] Google says it paid out $1.8 billion last quarter to AdSense partners, and another $400 million to “certain distribution partners and others who direct traffic to our website.”

Google is making aprox. 5 times more than content producers by indexing their content. It is the living proof that content aggregation can be profitable.