There are reasons why Google chose Samsung for their second, third Nexus devices. They make excellent screen, camera, processors, etc making up great android devices.
But now that they acquired Motorola, their fourth one will reveal what their real intention is on Motorola purchase. Other makers are already wondering and worried that Google will favor Moto for future android updates, features. I certainly hope things don't pan out like that as that will hurt openness of android and other phone makers will start backing away from it. I don't think Google can build Apple like ecosystem with only Motorola.