Again, who says it's suppose to show every death?
It doesn't show deaths where you died and noone was awarded the kill. If it did you would see more deaths than kills in the stats, but looking at tour 41 the stats say:
"All planes have 544369 kills and have been killed 544369 times."
Sure, you can break this down into individual planes and vehicles, but adding them up, they always equal up to the same. Now if stats showed every death, the second number would be higher, since SOME planes are bound to crash by accidents, but them being the same, it must mean that it only counts in the stats when the system counts a kill, not when a player crashes on his own. That way one can't increase without the other.
You can't compare the score and stats directly, because score counts all your deaths (killed, captured, bailed), while stats only count the number of kills made on you.
I don't know how else to explain it. It may not be ideal (I would have preferred the stats to be counting everything as well), but it is consistant when you know how it works.