Considering you can up, die, up, die, up, die, in a perfectly normal GV fight within 5 minutes and be happy, while possibly getting some kills yourself, it doesn't compare to airplanes. You'd be surprised the numbers the Panzer got back when it was the main ride. Something like 30,000+ kills per tour if I recall.
It's because the 2 games are totally different in the dynamics of how you play them. Sorties take a lot longer in airplanes, and because of that you're going to have less deaths (and somebody somewhere is getting less kills) so the overall numbers are much lower.
This is just pulled from memory, but I did some personal comparisons a while back before all the new tanks were added (after T-34/85, though).