Google's main source of revenue is their advertising business. Groupon figured out how to engage local businesses, many of which have no other online presence,

Google's main source of revenue is their advertising business. Groupon figured out how to engage local businesses, many of which have no other online presence, in a form of internet advertising and make a large amount of revenue in the process. Google being the #1 company in internet advertising, they are naturally very interested in what Groupon has achieved.