Remember, in the past they all rolled their own OS's for their phones. It was one of the main distinguishing characteristics used to differentiate themselves in the market from other manufacturers. That is why Google allowed manufacturers to skin Android in the first place and why they all continue to try to “make the OS theirs” with Blur, Sense, Touch Wiz, ect.”
I’m sure the open source hacking nature of Android also has all the manufacturers spinning like tops. It is imposable to provide support and good warranty service if people have the ability to hack whatever they want onto a device. Most people who root and flash understand that they are giving that up as a matter of course, but we have all seen threads asking… “I just bricked my phone, how can I replace it under warranty?”
The trend of Moto locking their bootloaders with tougher and tougher algorithms is a step in the direction of maintaining control over their hardware. The manufacturers and carriers do not view it as your phone, they view it as their phone that you are licensing and subscribing to use. (Not a reality, just the way they view the relationship.)
It will not surprise me to see Moto, HTC and Samsung all eventually lock their systems down tight and the skin customization will get even sillier then it is today. Eventually someone will realize that there is a market for unlocked, hackable high quality hardware and start making a line of phones for that purpose. Not just the Nexus line.
I’m just spit balling, but I could see Richard Branson getting into the handset business with a Virgin line of hackable handsets. Just imagine the marketing potential surrounding hackable Virgins.

It would not be hard to do, set up a list of specs with COTS parts, contract the manufacturing, walk it through the FCC (which should not be hard since everything is COTS) and market it. The big non-part costs would be the marketing.
Anyway, back on topic, Moto has always wanted tight control over everything they did. I did some work with them back in the day and “conservative” would be an understatement of their style.