You've missed the point of my post. GOOGLE doesn't control the update process for devices that they don't sell themselves. Samsung controls the update process for Samsung phones, which then goes through carrier certification for carrier-branded devices. Same goes for HTC, LG and Motorola (though now for fewer devices as only the "Droid" devices are carrier-specific - for Verizon). Samsung, HTC, LG and (to a lesser extent) Motorola have sales agreements with the carriers, those agreements include stipulations for OS update certification as well as add-on apps that need to be included. Unless Google strong-arms the manufacturers to start stepping away from those kinds of agreements, it'll never happen. One of the benefits to Samsung by having these agreements is that their $800 phones are more attractive on the pricing as it's spread out over 2 years.
Google actually tried direct-sales a few years ago, I think with the Galaxy S4 and a couple other devices. They were not carrier-specific and they did not have manufacturer overlays, it was called "Google Play Edition" and Google sold the devices for the manufacturers. It must not have sold well as they abandoned it after a year.
This is from HTC but it applies to all devices, even Nexus devices, read it carefully.
http://www.htc.com/us/go/htc-software-updates-process/ The only thing is, for Nexus devices there is no carrier certification, no OS overlay to re-design and Google is testing against the hardware they have specified as well as tested with during the preview phase such as with N. Consider the Nexus devices the iPhones of the Android world, it's just that the OS is open to other devices being used with it. Notice the only devices the N preview is available for are Nexus? That's because those are a controlled group as it relates to hardware and any software overlays (or lack of).
Think of it this way, if Apple allowed other manufacturers to build devices to use with iOS, the update process would be VERY similar as those manufacturers would have to test the new OS against the hardware in their devices. The only way for everyone to get updates quickly is to control what hardware the OS is running on. That would end up making the platform bland.
I don't understand why people feel the need to vilify Google on this. Samsung has an OS called Tizen in its back pocket that could replace Android if Samsung felt the need to spite Google, Tizen already runs on some of Samsung's smart watches. The fragmentation is caused by the phone manufacturers, and the chipset makers since they need to provide support for new versions of Android before the device manufacturer can update the OS.