The reason the defender wins boils down to basically 2 points:

1) The losses on both sides is proportional to the product of their power over the sum.

( A x D ) / (A + D )

To use numbers: 

10% of 90% of the total force equals 9% loss, as does 90% of 10%. 

90K power attacking 10K power will lead to both sides losing 9K

Note: there are times when this equivalence does not strictly hold true because of "siege mechanics".

Last I heard: siege mechanics were not applicable to raids.

2) Defending a town with fortifications will add power to the defense that does not result in additional points for the attacker, but will cause additional losses.

Thus it is possible to lose in a 9:1 mismatch, and still earn more points.

There is also a 3rd point, which may or may not come into play, depending on the forces involved:

3) Points for troops are awarded for their contribution to the battle, and not for the intrinsic value of the units.

This means attacking an offensive force of equal size will lead to a 10:1 advantage, and the corresponding losses for each side, but not a 10:1 rewarding of points.

All other things being equal: 1,000 AH-72s attacking 1,000 AH-72s caught "on the ground" will be a significant tactical and strategic victory, but the war mechanics may present it as a loss.

This makes the winner of the exchange the loser, and the loser comes out as the winner.

Outside the game, this would be akin to 1 boxer throwing a knock out punch with the first blow and when the other guy wakes up finding himself declared the winner because he hurt the hand of the guy that punched him, thus doing more damage per punch because he didn't throw any.

As ridiculous as you might feel the boxing analogy result might be is how ridiculous many players feel about "not earning full points" for killing troops via exploiting their weaknesses.