Statcounter doesn't count users, it counts raw hits. Both numbers are relevant for different reasons. If you agree that Chrome users surf more this could easily account for most of the difference.
That is strange, because Net Apps also counts the iOS browser (iPhone, iPod touch, iPad) as something like 50-60% market share, when there are only 400 million iOS devices and 500 million Android devices. I doubt the majority of Android users have never used the browser.
(1) I've heard the old Android browser on some phones can report it's user agent as safari or some generic looking webkit that might get folded into safari numbers.
(2) site bias? Purely as an illustrative example imagine if Apple.com was one of the sites in Net Apps network while Android.com was in the Statcounter network.
(3) actually accurate. The wikimedia numbers are 10% mobile safari and 4.5% android.