netmeg - 10:44 am on Sep 3, 2012 (gmt 0)
Over the years I've noticed as much as 20% of traffic (and transactions) missing out of Google Analytics. Whether or not they won't disclose it or they can't, I have no idea (the amount that gets chopped out seems to vary over my many sites)
They don't claim to be 100% accurate, and if you manage to grab ahold of someone privately, they'll tell you to consider GA as something to reflect trends, and not 100% of your site stats.
(Implied but not stated is "what do you want, it's free")
It is what it is.