Exactly. If they get a few dangerous drivers off the road, well, that's just a nice side benefit. That's why you never admit anything to a cop, and never, ever, ever show up in court without a lawyer. Judges don't like people who aren't greasing the system. They were lawyers once too. Call me cynical, but I'm also realistic.
I'd say you hit the nail on the head. Even if you are going to plead guilty, you should spend the money on a local lawyer to show you are playing the game. If you plan on fighting a charge, it's best to try and get an out of town attorney who doesn't have to worry about irritating jugdes/prosecutors he works along side on an ongoing basis.