to expand their customer base.
on a really high level: Google's direct customers are business who want their ads to find specific demographics. that business will grow as long as more businesses sign up for that service... which hinge on a growing base of targeted demographics.
i think for first world countries, computer sales have reached a peak. basically everyone who wants one, can more or less obtain one through various means. In order to capture another revenue stream Google had to figure out way create another "service" through their existing end users (consumers). going mobile was the logical solution. people spent X amount of time at home with their desktop/laptop but a cell phone can be carried everywhere.
one problem: smartphones were expensive because they weren't a commodity like dumb phones that Samsung and LG were busy pumping out every month. prior to the iPhone you had Palm, Blackberry and Windows Mobile that were never going to reach any meaningful volume for Google to direct their ads. the iPhone's price + service plan easily placed itself out of a lot of people's reach.
solution? commoditize smartphones. let's not mince words here, for all the following that Samsung and HTC have developed over the years, none of that would have been possible without Google. another bonus was that the two companies tend to operate like traditional PC manufacturers in that they had to release large quantities of products every quarter at low prices in order to make sales. a short product life cycle + free OS software all but guaranteed commoditization. look who joined the fray: Samsung, LG, HTC, SonyEricsson, Huawei, ZTE, Motorola. how many actually made money as the competition intensified? Samsung and HTC*.
now most carriers low-end phones are Android phones and not feature phones. that price point puts it in reach of a lot more consumers than the iPhone. all Google had to do was to wait for a couple of contract renewals, during which carriers transitioned to a smartphone dominated product line up.
in the US, the phone mix is roughly 30% smartphones. 30% of 300M is a good amount of people. a whole new "indirect" revenue stream was created.
however, that's just my own theory.
And I know what all of you are going to say: Keep Apple on their toes. While I think that's debatable, it's immaterial. I referring to Android's business model. Look at from that perspective, not as a consumer.
Google made hardly any mention of Android in their quarterly earnings release. I fail to understand what Android does for Google financially. What does Android add to their bottom line?