You hardly can get better if you're not fighting better opponents.
Rank is easy to manipulate - in both directions. It has very, very little to do with actual skill.
...so you keep tweeking the formulae until you get the disired results...namely better retention of noobs, and happier campers in the expert arenas.
In answer to your other post, the noobs would learn on Titanic Tuesday from the vets.
To answer your other post, the only way to manipulate your score backwards is to let yourself get killed. Do you think people would let themselves get killed so they could level down so just so they could get kills they could have gotten in the level up arena if they weren't letting people kill them? Not really sure it matters either way though, because the point is not to determiine how good pilot is based on what arena he ends up in, but to create different playing evironments based on how well a pilot plays the game.