I'm "superb" (15%+) which makes sense, as I hold gunnery in very high esteem. I never vulch, or fly tater slingers so that isn't the reason. In a MA packed with people gunnery is perhaps the most important skill, so as to kill as quickly as possible. Next would be SA, then the actual flying skill itself...
I agree the stats are interesting. I did a similar breadown a while back for my own amusement and got exactly the same average 3-4 years ago. From my own subjective observations I will say that the vast majority of people I run into are definately spray n' prayers which would account for the low average hit %. Then there's the folks who shoot at ground stuff in fighter mode. As a rule of thumb I will always score as attack if there's a chance the sortie will take me near the enemy's field, solving that dilemma. But, then again those that vulch want to be in fighter mode for the vulchfest...