As VentureBeat notes, Amazon's Web Services (AWS) division provides the hosting that powers six to eight of the top ten Facebook games, according to AWS' Jeff Barr. This means companies like Zynga, Playfish and Playdom pay Amazon substantial sums of money so they don't have to worry about things like server maintenance, bandwidth, backups and security for their growing game. Those substantial sums have helped make AWS into a $500 million a year business for Amazon, according to some estimates,
Of course the relationship isn't perfect -- problems with AWS scaling are likely behind some of the outages that occasionally plague many growing games. Still, Amazon has positioned itself well to benefit both from online sales of disc-based games and from the growth of web-based games.