The D-hog is heavily used for jabo, so it's k/d is meaningless.
The tags force pilots flying perk planes to avoid big fights, avoid situations where they'll be outnumbered.  So why is it a surprise that the k/d ratios are higher?  The pilots are forced to avoid large fights, and stick to easily winnable ones.   Any plane perked would have it's k/d go way up, simply because it's perked.  
If you perk the p51d, dora, 109g10, or la7 thier k/d's would go through the roof for the same reason.  You don't see the problem with the spit14 having only a slightly better k/d ratio than it's free cousin, which is the second most used plane in the MA?
Oddly enough though, the f4u-4's k/d has gone WAY up this tour.  Past tours it's k/d has been well behind the f4u-1c.