Unless Google can come out with something innovative through their ownership of Motorola, Google is doomed to lose this.
In the Android space, it's wise to divorce Google from Android to really understand what Android REALLY is. Android is open source and can be used by anybody. This has left the playing field open to the likes of Amazon to do the Kindle, which despite adding market share for Android, does absolutely NOTHING for Google. Same goes for the Nook, Android on phones sold in China & other places where Google services are restricted by default. While Android makes up 90% of smartphones sold in China (most by Lenovo & Samsung), how many offer Google services?
Google has not been able to monetize Android in any meaningful way. Samsung has & it's why they are the only truly profitable Android vendor. This should worry Google, as more people associate Android with Samsung rather than Google. Oh, and lets not forget that Samsung & Intel have been working on their own open sourced OS, Tizen.
Eventually, Samsung will tire of Android, as Amazon will, as well. Right now they are a means to an end & that end is in sight. Samsung realizes that they put the effort in making Android actually useful, release devices and then sit back & watch Google try & take over with Google's services, such as the Play Store. Do you think Samsung likes this? Nope. Not. One. Bit. No company would.
Nexus devices have a very minute penetration into the market. Which is the nice way of saying "nonexistent market share". What started out as a developer phone, needs to mature into a mainstream mobile device if Android has any chance of survival.