Google continues to enjoy a unique position in the mobile space -- they make money off of pretty much every platform. If you use their own, freely licensed Android platform, they earn revenue off of advertising. If you use anyone else's platform, including Apple's iOS on the iPhone or iPad, Google still earns revenue off of advertising.
Recent Nielson numbers claimed Android owned nearly 50% of the US smartphone market. Google, however, owns the vast majority of advertising revenue on nearly 100%.
According to The Guardian, since 2008 Google has earned $550 million from Android, or roughly $10 per device per year. (Since Google gives away Android licenses for free, that money likely comes from advertising related to search and other services). By contrast, Google is estimated to earn $30 per PC per year. What's more, Google CEO Larry Page recently claimed revenue from mobile was now running at $2.5 billion. So $2.5 billion minus $0.55 billion leaves roughly $2 billion in revenue from other platforms. And given market share, much of that would likely be iOS.
Marketingland calls foul on The Guardian's numbers, however, saying there's no way to tie settlement valuations to earnings figures from Android, and hence no way to determine what percentage of Google's mobile revenue comes from iOS vs. Android.
Update: Asymco weighs in and thinks the numbers might not be far off.
Many of these figures begin to "hang together" as we balance assumptions about costs, revenues and statements made in public. There is a consistency within a comfortable margin of error. If that is the case, then the economics of Android begins to take shape.
So in terms of returns, Android is sustainable. However, in relative terms the value created leaves much to be desired. Whereas Android generates $1.70/device/year and thus an Android device with a two year life generates about $3.5 to Google over its life, Apple obtained $576.3 for each iOS device it sold in 2011. The economics of Android are nothing like the economics of iOS.
For the sake of argument, even if they're not 20/80 but closer to 50/50 or even 80/20, that's still a huge amount of money to make from a competitor's platform, and a huge competitive advantage.
Apple, of course, makes no money from Android users. They offer other platforms precisely nothing in terms of services or software. While you can get iTunes on Windows, you can't get mobile iTunes Store.app on Android or any other platform. You can't get the mobile iWork or iLife suites. You can't get iBooks. You can't get anything.
While the iOS App Store plays host to several apps from Google (and Microsoft), Google play (and Microsoft Marketplace) have exactly nothing from Apple.
That means iOS users have absolutely the best choice when it comes to mobile software (what else is new?), but it also means Google (and to a lesser degree, Microsoft) have revenue opportunities beyond their own platform.
That's part of the reason Android exists. Google originally fielded Android in part so that it could never be frozen out of mobile, where they and everyone else saw the future was headed at an accelerating pace. Back then, Android was meant to compete with Windows Mobile, and the potentially dominant Microsoft cutting out Google and using their own services was a legitimate concern.
Then the iPhone happened, and with it the mobile web happened in a way never possible before. Microsoft's mobile future suddenly dimmed sharply, and Google responded, smartly, by doing an about face and making taking Android decidedly in an iPhone direction. Whether or not Apple would ever field a Google competitor remains in question, but Google fielded an Apple competitor. It caused a schism to the degree that the late Steve Jobs vowed "thermonuclear war" to stop what he considered to be "stolen property". It also gave the carriers a powerful OS to do with as they would (and if we can agree on anything, it's that the carriers are more "evil" than Apple and Google squared).
Now, four years later, despite attacking Apple as being the enemy of openness, despite giving control of the user experience back to carriers, despite creating an uncertain update and compatibility environment for a growing segment of the smartphone market, Google remain the default search and map engine on iOS, and iOS remains a valuable revenue source for Google.
Sure, Apple could one day flip a switch and make a different provider the default search engine, and even with the market dominance Google enjoys, that would hurt. (For some percentage of users, settings don't exist and whatever is the default remains the default.) Yet, ironically, it's Android itself that's made that more likely than it may otherwise ever have been.
Still, for now, the more users Android gets, the better for Google. The more users iOS gets, the better for Google. The more users anyone gets -- with the exception of forked variants of Android itself, like Amazon's -- the better for Google.