Yup, I love that the correlation for "Facebook shares, like, comments" (though those are three different things) is listed as 0.03 less, even though I've pointed out multiple times that Facebook doesn't exactly make it easy for Google to crawl Facebook to see that data.
Your point #3 is critical: high quality things get more +1s (and tweets, and Facebook likes or comments or shares).
Your point #3 is critical: high quality things get more +1s (and tweets, and Facebook likes or comments or shares).