Android instability
If you were a PC OEM from, say, 1990 to 2010, you operated in a very clear ecosystem. You outsourced much of the innovation to Microsoft and Intel. You knew exactly what WinTel were doing, both because their roadmaps for the next few years were actually public and because Microsoft and Intel had very clear and widely understood strategies. Moreover, the core, fundamental strategies of OEMs, Intel and Microsoft were pretty much aligned. Everyone wanted more PCs to be bought, and preferably a good number that were high-end and high-margin. Intel, Microsoft and CloneCo all lived for the same things. CloneCo didn't necessarily make great margins (and eventually got killed by Dell, perhaps), but it knew what the game was.
The Android ecosystem today is superficially similar to the PC ecosystem, but I'd suggest that the clarity and alignment of interests of the PC ecosystem isn't present in anything like the same way. As an Android OEM you have very little idea what Android will be in 3 years - partly because Google itself may not have a fully-formed idea. There certainly aren't public roadmaps stretching out years in advance.
It's also questionable how much alignment of interest there is. Google certainly wants Webkit everywhere, and arguable Android everywhere (or, more precisely, Google Plus everywhere). But that doesn't translate to a burning hunger for an aggressive phone replacement rate at high prices. Indeed, Google Play Services reduces Google's interest in device replacement as a way to drive service penetration. As an Android OEM, your ecosystem creator doesn't benefit directly from the health of your industry. A healthy PC market was Microsoft's driving objective - 'A computer on every desk and in every home'. That's not quite the case for Google and the sales of Android smartphones - they're reach, and a means to an end, but not the reason why Google exists.
Next, it's not clear what a sustainable position for an Android OEM looks like. All the brands except Samsung are sub-scale and failing, and while Samsung looks dominant it is clearly feeling paranoid: the growth of the Chinese Android OEMs outside China is a huge question. Lenovo has made its first move by buying Motorola but the real story is whether 2, 10 or 100 others follow it, and if so how.
Finally, Google's control of Android itself is a question. Amazon forked it, but with limited broader effects. Almost all Android in China lacks Google services but then Google is largely absent from China anyway. The ways that forks of Android might become relevant outside China (and Google's tools for preventing this) are complex and a topic for another post, but we can't rule this out. Indeed, a lot of the most interesting ecosystem innovation is being done on top of Android rather than as a would-be competitor to it.
On one level, then, the smartphone platforms wars are over - iOS and Android both won. But actually, nothing is finished - we just move onto new questions.