In BF2 we have vehicles and much bigger maps.
A jet pilot with a couple of thousand hours in (400 in jets) can easily get a KD or 40 or 50/1 if there are no equally skilled pilots against him. In maps where one side has a carrier, if the pilot is hit he can easily repair and rearm in seconds then go hunting again. Against the best pilots, you don't even want to get into a tank or APC because they are larger targets for jets.
We do have some servers set to infantry only. But in Battlefield we also have a medic class which can heal wounded soldiers. So if you play in a squad with a medic against incompetent opposition, you can wrack up a high count.
My best Infantry Only score was 36/3 my medic revived me maybe 6 times. And many things factor - in BF2 commanders can spot enemies for you which really helps, medics can heal you, etc.
So am I a 10:1 KD player - not at all, but I've gotten lucky sometimes, and unlucky others.
My KD is directly affected by the level of competition I face. On my own clan's server, if I am playing against my better clan mates, they clean my clock. But they play in a competitive league. If I take those same skills to a "vanilla" server I do very well. But I actually prefer the competition, I've unlocked every weapon and at this point I'm just having fun.
Of course there are cheaters. Now with the recent changes to punkbuster we ban 1 or 2 a day on 3 servers. We also get glitchers - people who find holes in solid walls etc, but we usually track them down and ban them as well.
But the point is that for every hackusation, we find few hacks users. We ban many more people for blatant disregard of the server rules or stats padding.
James