Two years ago, Page created a bunch of separate product groups within the company, each led by an executive who reported directly to him. At the time, Android was one group. Chrome and Apps was another.
Until a year ago, the Android team didn't even use Chrome—it had its own Android Web browser.
Google has slowly been rationalizing similar disjoint efforts. For example, it rolled together several digital-download stores into a single Google Play store for apps, e-books, and music.
Expect more rationalization to come. Pichai now oversees all of Google's operating-system efforts—ChromeOS for laptop and desktop computers and Android for mobile devices. Those are probably headed for unification, as are Google Play and the Chrome Web Store.
And expect an even greater emphasis on Android devices running a standard set of Google apps—Gmail, Google Maps, Google Drive, and others.
Putting these organizations together isn't just some kind of random corporate reorg. It's a rational move that recognizes that most of the value Google offers in mobile devices is in the software it provides above the basic operating-system level—software that will be woven deeper and deeper into the Android experience.