No, it is just that the surviving men are the ones who actually killed a lot.

If you happen to get a heavily depleted cavalry unit, use it to chase down routers and you are bound to get 2-3-4-5 upgrades in experience in a single battle. It is terribly easy to do. Then you just retrain it, and voila, you have an instant gold chevron unit.

I don't like that, but what am I to do? I use my units to the fullest. Am I to let the enemy escape or disband a unit so as not to get hugely experienced units that I didn't earn? Bah!