Google is moving in many directions—mobile, browsers, productivity apps, operating systems, social. At first glance, it may seem like it is trying ever so hard to move beyond it's giant one-trick pony : search. What people keep forgetting is that it is a pretty good trick . Benchmark Capital VC Bill Gurley reminds us how good this trick is in an excellent post that looks at Google's market expansion strategy not as one of a series of aggressive offensives, but rather a highly defensive strategy. Warren Buffet famously describes the best businesses as "economic castles protected by unbreachable ‘moats.’" Search is Google's economic castle (perhaps with other forms of online advertising such as display thrown in there), and everything else is a moat trying to protect that castle. Android is a moat. The Chrome browser is a moat. The Chrome OS is a moat. Google Apps is a moat. These are all free products, subsidized by search profits, that are intended to protect the economic castle that is search.