In war its called a inserting a mole or 5th column, in the movie “Social Network” a main character called it “The Little Big Horn” strategy. Google has turned to it as a way to to pull in iPad and iPhone users to Google+ slow starting Google+ service before it becomes a non-starter. They are probably thinking that If it didn’t fly as first planned then you must go where they are.
Google can always snatch up OS dependent Android users as you need but by pre-emptively snaring Apple users Google can establish through an app their brand as cool and in essense beat Apple to the game.