By Nilay Patel and Dieter Bohn

This Thursday, we expect that Amazon will be unveiling a least one new Kindle Fire alongside a new e-reader. If you believe Amazon’s somewhat fuzzy math, the Kindle Fire is far and away the most successful Android tablet on the market, but it's a strange kind of boast: the Fire runs "Android" in only the loosest sense of the word, as an underpinning to Amazon's ecosystem. The Kindle Fire is an Amazon content delivery device, not an Android tablet.

Based on the leaks we’ve seen of the new Kindle Fire’s interface, Android's been buried even farther into the background — a casual user may not even know that it’s there. Android on the Fire is about application compatibility, not Android itself, and it highlights Amazon's decision to fight a battle between ecosystems, not operating systems. But that's not such an easy choice to make, and Amazon's success with the Fire just highlights the uncomfortable truth for Google: Android's failure on tablets has created an enormous opportunity for Microsoft.

Just 'having an Android tablet' has basically been a non-starter

There are many reasons Google's massively successful phone operating system has basically fizzled on tablets — uninspiring hardware and bad third party software chief amongst them — but ultimately the biggest problem is the lack of a single Android tablet ecosystem worth anything to consumers. Launching a successful Android tablet on the merits of "having an Android tablet" alone has basically been a non-starter for everyone who's tried. Amazon's key insight with the Fire was to use Android as the means to enable another ecosystem that provides value to consumers, and everyone else is racing to adopt the same model — even Google. What is the Nexus 7 but a window into Google Play? If anything, the Nexus 7 and Kindle Fire are the Android answer to the iPod touch, not the iPad — devices excellently suited to consuming media content and running phone apps, but not anywhere close to laptop replacements.

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What is the Nexus 7 but a window into Google Play?

Even historically hardware-focused companies like Samsung and Sony tried to get into the act last week at IFA. Both companies are touting their own attempts at building an ecosystem — the "S Ecosystem" and the not-yet-realized "One Sony" respectively — and both companies are probably overselling what doesn't really exist. But it's better than conceding the obvious: putting an Android tablet on store shelves without the promise of a rich cloud-backed ecosystem outside of Google's own is a recipe for failure. Watching Sony and Samsung insist that they have valuable ecosystems draws Amazon's success into sharp focus: the Fire is truly boring hardware backed by a beloved set of services, and it's turned Android on its head.

Is this what Google envisioned when it created Android? Not quite, but it's not diametrically opposed, either. With Android, Google wasn’t playing to win — it was making sure it didn’t lose. As court documents in the Google vs. Oracle trial confirmed, in 2005 Google was much more worried about a Microsoft hegemony in mobile than it was about Apple:

It is widely believed by that if an open platform is not introduced in the next few years then Microsoft will own the programmable handset platform: Palm is dying, RIM is a one-trick pony, and while Symbian is growing market share, it's becoming a Nokia only solution.

Google realized a common platform for multiple OEMs in mobile was inevitable, and wanted to ensure that it wouldn’t be locked out. Ultimately, Google was much more concerned that the common platform would be a proprietary solution like Windows Mobile than it was about Android fragmentation. Google may have some heartburn about OEMs and carriers failing to update devices and its lack of presence on the Fire, but it’s surely better off than it would have been had Microsoft managed to get its act together sooner.

Google's strategy worked brilliantly on phones, but the window for success on tablets is closing

Google's strategy worked brilliantly on phones, but the window for success on tablets is closing rapidly. After all, most Android OEMs are also Microsoft OEMs, and Windows 8 and Windows RT have enormous potential to succeed as proper competitors to the iPad. And the value proposition for OEMs is strong: why spend money on building Android up into a laptop replacement when Microsoft is already spending billions developing Windows? Why try to create an independent ecosystem to compete with giants like Apple, Amazon, and Google when you can just tap into the enormous base of Windows customers? Why continue to dance around the sorry state of Android tablet apps when an explosion of Windows don't-call-it-Metro apps is looming on the horizon? And, perhaps most cynically, why continue taking the risk on Android tablets when every major Android OEM is paying patent licensing fees to Microsoft anyway?

What the Fire has taught us before and will teach us again this week is that the biggest threat to Android tablets isn't necessarily the iPad — it's that the companies which make the devices aren't totally invested in ensuring the Android platform succeeds. The difference now is that Android OEMs finally have a viable alternative in Windows, and Google needs to either commit itself to true tablet success or watch from the sidelines as Microsoft mounts the first serious challenge to the iPad.