muzza64 - 8:54 am on Aug 10, 2013 (gmt 0)
I don't think the data collected by GA is at a sufficiently detailed or granular level to be an accurate indication of even an individual site (unless they collect much more detailed stats than are displayed in GA). I use another tracking system which is much more accurate but it has a limited functionality so I use that for the headlines and GA as a rough guide to everything else.
I agree that Google is collecting usage data from somewhere and employing it in the algo to a certain extent which may increase as their confidence in it grows. Whether its Chrome, ISPs or what I don't know or care really. I just know if I were Google I'd want usage data and I'd pull out all the stops to get as much as I need for it to be meaningful (and try to prevent rival search engines getting it).
Just look at Googles efforts in the mobile market. Why do they want everyone to use an Android device? Data collection is my bet. As the world migrates from the desktop to the mobile device they face new challenges in accessing data. Data is like oxygen to search engines. If you can grab all of it and starve rivals of it, the rivals will eventually die.