Google has already said it several times, but it seems with more rumors about the Motorola X Phone and how it's heavily influenced by Google, they want to come out there once again and say that there's a wall between them and Motorola, and they are treating them pretty much like any other manufacturer.
"We treat all of our partners fairly," he said. "Motorola we consider a partner just like HTC or Samsung."
When it comes to Nexus devices, I'm sure that's true. In fact, they probably even treat Motorola worse in that case, because they don't want others to believe the Motorola is a favorite in that competition for who's getting the Nexus brand. But they also don't even need Motorola for Nexus devices, at least not any time soon. Why do that when they can just make sure their future Motorola devices are as good as Nexus devices? Plus they are not limited to just one phone, but as many as they want.
From that point of view there isn't really a wall between Google and Motorola, nor should there be one. I really believe Google should be fully involved in making Motorola devices as good as possible, and use stock Android on them (nobody else seems interested in doing that anyway). And they need to do that if they want Motorola as a phone company to survive.
With a great design, build materials and specs, Google could make Motorola phones at least as demanded as the Nexus 4, which hasn't even reached its true potential because Google expected much fewer sales. They now say they have fixed that, so we can expect them to be more prepared next time.
However, with the Nexus devices at least they seem pretty confused on whether they want to go cheaper, or add more/better features. On one hand I could see them trying to make them even cheaper with good specs, maybe so they can help their partners sell millions of them. But in the same time, I wouldn't like that at all, unless they want the Motorola X line-up to replace Nexus at the high-end. That would make some kind of sense for both Google, because they'd rather promote their own high-end stuff, and also manufacturers because they usually want to promote their own high-end stuff over Nexus anyway.
Still, my hope is that Nexus would turn into a program of "stock Android devices", that also includes all Motorola devices, and Google works on getting as many manufacturers as possible to sign-up for that program, too. That program would have dozens of Nexus devices, but all upgrades would be handled by Google, and they would ship under stricter requirements. Think of it like Microsoft's own WP OS, where there's one UI across multiple devices, and all are upgraded by Microsoft. Nexus could be that for Google.