This rumor's been floated since the start of the year, and to be honest I don't have much visibility into the possible reasons behind it. What this basically means is that it seems like Google is giving up on making their own hardware in order to reign in third party software customizations. Android Silver seems like it'll be an expanded and more well-marketed version of the Google Play Edition devices. It's possible Google thinks Motorola can pick up the slack for high-end, low-price "stock" Android phones.