When Motorola introduced the Moto X, one of the angles Motorola took in making their sales pitch for the device was how software features could be more useful and valuable than top of the line specs in a smartphone. To drive home this point, they included a variety of features including one originally called Active Display, now Moto Display, that would cause the display to turn on when a notification was received or when it detected the phone had been picked up. It looks like that same feature has found its way into the Nexus 6.
A screenshot of some display setting for the Nexus 6 shows an entry for a feature called “Ambient display” with a description that reads “Wake screen when device picked up or notifications arrive.” This seems to clearly suggest Google benefited from having Motorola produce the Nexus 6.
On the Play Store page for the Nexus 6, there are a couple entries that include a reference to “Ambient Display.” The entries outline the potential impact on standby time for the device if Ambient Display is turned on, which appears to be about a 25% reduction. Despite the hit to battery life, the feature is considered a great convenience and difficult to give up once one gets used to it.