I'd offer a guesstimate of 75% or better are the result of camping. Very few maneuvering tankers out there, but there are some great static shots in the game. 
Very true, less then 10 tankers I know of that could maneuver and hit a moving tank under 2k at full speed. Pretty slim numbers, I would say barely 20 or so tankers could sit static and hit a target up to 2k in 1-2 shots.
Overall tanking has always had 60%-75% on defense vs 30-25% attacking, mainly because you have aircraft and ords at your disposal, where an attacking force has easily less then 30% numbers to attack with, unless ords and VH go down then these numbers can dwindle down to pretty much nothing once the defenders get into a camping position.
Often more then none if ords are taken out, the ground attackers can overwhelm defenders if they arn't prepared (for example the common tank battles like V86, V135 from previous maps)
Most people will not go on the offense in a ground vehicle and I am not sure exactly why, but I would pin it on the lack of support or airpower.
I rarely have seen an evened out tank fight, only 4-5 times a tour this will happen, mainly one side will make a push and continue the attack, where most attacks will decline after the first failed take.