Google works on an input/output system. In other words, for everything that Google developers create, Google accepts input from users and developers around the world. Note that the latter group/community is orders of magnitudes larger than the former, so by harnessing the resources and power from the users and developers around the world, Google's Global footprint becomes significantly larger.
For instance, Google produces continuos output in the form of products and developer platforms, and accepts input in the form of development directions and most importantly, apps. By creating platforms on which developers can build on top of, Google harnesses the users that want the apps. The more that Google releases (e.g. SDKs), the more developers are looped in to create new apps, and the more users get pulled in to use the apps, thus acquiring the Google products in the process. Thus, the number of people around the world that are increasing the consumer base for Google products far extends past the number of Google employees.
In fact, the number of people indirectly working for Google is huge. Consider the Google Developer Groups (GDGs) that can be found all around the world - independent organizations of developers and enthusiasts that get-together to bond over Google's technology (they also give Google product-related talks and host help sessions for their local communities, all on their own time). What's in it for the members? Members of GDGs have the support and network of individuals with similar interests. Google wins by having a Global network of communities that are self-sufficient and self-reinforcing and do not require Google support or investment. Google Trusted Testers are non-employees that test beta products for Google. What's in it for the testers? First-hand experience with Google products. What's in it for Google? A workforce for whom being "first to try a product" is sufficient reward. The Google Student Ambassador Program gives college students an opportunity to exhibit leadership by acting as a liaison between Google and their home institution, putting on Google-supported events (information sessions, hackathons, etc.) and forming student communities. The student ambassador's motivation is a nice line on their resume and great experience communicating with both industrial and institutional personnel and organizing events. Google wins by being promoted on college campuses and having easier avenues for student recruitment... all for the price of providing some Google-themed freebies at college events. Then there's all the other smaller organizations that are not directly supported by, but have affiliation with, Google. For instance, the Google Anita Borg Alumni Planning Committee that I am part of is devoted to increasing visibility and interest in computer science among minorities and help promote diversity in computer science education. We, as a group of females distributed Globally, start initiatives and put on events (such as the following) in our local communities to advance these missions. Google provides the branding. We win through affiliation with Google, Google wins through affiliation with philanthropic organizations. These are just a few of the organizations and communities that are affiliated with but not directly supported (at least financially) by Google. In fact, Google does not need to directly support or control/govern any of these communities precisely because they are self-sufficient and self-motivated - a big win for Google, given the limited investment.
Now consider the yearly Google I/O conference that draws over 5,000 attendees. Many of these attendees are developers who come to the conference to hear first-hand about new product and platform releases (and participate in hands-on workshops with the Google product developers themselves). These developers then bring this knowledge back to their communities, and contribute their own apps and products to the Google community. Each year, at this conference, Google announces new support infrastructures to make the use of Google products increasingly easier (this year, for instance, Google announced new OS and language support for the Internet of Things so that developers can more easily add mobile support to physical objects - think: the smart home). Correspondingly, the number of Google product-driven apps increases and expands. Users of apps buy Google products and services and continuously provide feedback (either directly through surveys or indirectly by having their interactions and preferences logged on Google servers). Thus, we are all contributors to the growth of the Google footprint.
What can we infer from all of this? Google is firmly rooted in our societies and is here to stay. The number of people supporting, improving, and building on top of Google products is huge - it is Google's invisible workforce. Thus, Google will continue to grow and improve at great speeds.
What lesson can we learn from all of this? Being open (i.e. in terms of software and even hardware) can allow a company to harness the power of other developer and user communities, thus increasing the size of the effective workforce that builds the company's products, directions, and reputation. Google has one heck of a business strategy.