Also, Google wants to maintain a neutral status without favoritism with all of its OEM partners. It would be difficult to heavily promote the nexus 6 without a common perception coming about that Google is saying Motorola makes the best android devices.
I don't think Google is trying to stay as neutral as they have in the past anymore... This may just be the start of the Android Silver program we heard about and then kind of faded out... Maybe they just call it the Nexus program and we will start seeing more Nexus this and that phones from different MFG's on Google play......
I don't think they are out to dominate the market for Phablets or be an Apple who sells 10 million devices the first weekend... But I also don't think they are too afraid to upset the other OEM's as before.. Samsung has been toying with their own OS with Tizen.... They've already put in some more restrictive wording in the Android contract to make Google apps more up front and center and forcing anyone who uses Android to put their competing apps in the back ground (At least up front)
Android has been "Free" because Google makes their money on search, ad and services they offer... but these other OEM's have taken advantage of that and tried to push their own apps and services over the Google stuff... So why would Google who has more than enough revenue, profits and cash on hand... Worry about upsetting people who've been trying to make money behind Google's back? or create their own software (Tizen) to replace Android on their devices? or competing services to replace the Google ones???