Once again, you're missing the point. Android isn't about making sure Google has a stranglehold on mobile devices, it's about leveling the playing field. Sure, Amazon can release a device with Bing as the default search engine, but Samsung can release a device with Google as the default search engine. And as long as Google is better than Bing (which it is right now), people will prefer the Samsung device over the Amazon one, at least in terms of searching the web. And if Microsoft pays off Samsung to set the default search engine to Bing on their devices too, someone else can come in and make yet another tablet that uses Google, since their mobile OS development costs will have been nullified by Android being free software.
So your point is that OEMs will ship Android phones with Google services because they're better than alternatives? What if Microsoft pays Samsung to ship their phones with Bing, and they're still wildly successful? How does being the developer of Android OS help Google reach search customers? If the most successful Android OEMs were to ditch Google services for whatever reason, then Android OS development costs would be better spent directly paying OEMs to ship with Google services, and Google would have little reason to keep sponsoring Android's development.
You're forgetting a lesson we learned from Microsoft. When people in developing countries were pirating Microsoft software (Windows, Office, etc), Microsoft released lower-cost versions of their software to save some face, but in reality Microsoft just didn't care. Let developing countries pirate our software, the important thing is they're using our software. Which means they're not using competitors software. Which means Microsoft stays on top, in the mindset of the people, and when those countries become developed the people will buy legitimate copies of Windows/Office.
Google has this even better on Android. People aren't pirating Android, they're using open source software. And even if that software runs Bing or Yahoo search and the users like Word to Go rather than Google Docs and Outlook.com rather than Gmail, they're still using Android. Which means they're not using iOS. And chances are, they'll want to stick with the OS they know, so in the future they might end up with a more Google-ified device. Keeping them off iOS is the first step to having them as lifelong customers. Microsoft knew this, and Google knows this.
I think w1ntermute is trying to say that Google has commoditized their compliments (http://www.joelonsoftware.com/articles/StrategyLetterV.html). Google is benefiting not from control but by weakening lock-in. The barrier of entry to the phone market is much lower with android dominating.
Without high barriers to entry Google can count on churn in the phone market. Right now Samsung is king, before it was HTC, maybe LG will be next? Android thus becomes the defacto OS while phone companies fight over the hardware.
Don't forget that Google has a better advertising than Bing so they can offer more for the search deals. They can easily overbid Bing if Microsoft doesn't blow money into it again.
When there are a lot of players, they have the upper hand in bidding.
Actually Android isn't free. It is so patent encumbered (and hence requiring of royalty fees) that options like Windows Phone end up being a cheaper option.
This is a common misconception. Android isn't "patent encumbered". Certain OEMs have simply given in to Microsoft's legal threats and agreed to pay them to license certain Microsoft patents (regardless of their validity and/or relevance to Android, neither of which have been confirmed in a court of law) rather than burn money on expensive legal proceedings.
