Google has been very aggressively using their homepage to promote their products and services.
Right now they are promoting a link to New Gadgets on Google.com which points to a landing page showcasing products like:
Google Search service
Google Plus network
Google Android Market
Google Chrome Web Store
Google.com is one of the most visited web pages in the world and a promotion like this is seen by millions of web users around the world.
Google has promoted individual products through their homepage in the past like their Nexus branded smartphones as well.