Google Makes 1.5 million Books I'm Never Going to Read Available for Mobile

Google announced on it's Inside Google Book Search (yawn) blog that it will make all 1.5 million public domain books that it has made available for it's web search product available for iPhone and Android devices through a downloadable application service. Apparently optimizing the scanned text for easy mobile reading was a non-trivial engineering task. Cool I guess...but other than those interested in enhancing their nerd cred by claiming to have read a 300pg Sherlock Holmes mystery or an old textbook about silkworms on a G1, why would anyone want to do this? Is there an economic model here, or is this just a Google "Do Good" initiative?