I was surprised when Android was announced, because it didn't seem to fit with Google's principles. Not only was it client software, not cloud software to which Google had previously confined themselves, but it also created a new platform, separate to the web.
Google's search and ads have tied its fortunes to the web, and their management knows it. They dominate their industry so much that the only way to increase their revenues is to get more people using the web all the time. To achieve this, they they need not only to innovate themselves with web apps such as Google Maps or Gmail, but to nurture an ecosystem of Silicon Valley startups to work on web applications rather than on any other platform. They do this using a combination of Google Ads (providing revenues to startups), funding browser developers such as Mozilla, web developer evangelisation (such as spreading the word about Ajax) and careful purchases of the best startups.
Since Android was announced, this focus on the web has increased. Recently Google announced it is putting all its energies behind HTML5, to bring new capabilities to the platform such as video, geolocation and graphics. They have created a new browser, Chrome, and promoted it hugely on the Google homepage.
So why on earth create a new mobile operating system? Now they have to build a new developer ecosystem using the Android Marketplace. These aren't web apps, therefore Google doesn't get the same search or ad revenue. And it takes the focus in Silicon Valley away from the web.
Of course, there were good reasons for Android at the time - fixing the lack of good competition for Apple, persuading the network operators to invest in data networks, and attempting to fix the broken industry structure especially in the US. And Android is increasingly successful. But I still believe that it's the wrong solution for Google to the original problem.
Now Chrome OS is about to be released. It's another client OS, but this time the operating system is simply a web browser. No distractions from the web, no separate platforms, but still a way to shakeup the computing industry in Google's favour.
For once, I think Steve Ballmer was correct about Chrome OS - "It’s incompatible with the one operating system they have shipped. To me, still, I don’t understand why they needed another one. They must have gotten the first one wrong."
Despite it's current success, I think they did get Android wrong. There must be some huge arguments within Google about the correct model, but Chrome OS is the one that fits with the rest of the company. Time only will tell how the two operating systems sit together, but I wouldn't bet on Android surviving for longer than it takes to get Chrome OS powerful enough to drive a phone.