Not necessarily true. It applies if you get one of todays very popular, obscenely long term loans. A good old fashioned 3 year loan will keep pace nicely with depriciation. For this reason, a good rule of thumb is that if you can't afford payments on a 3 year loan, then you can't afford the car. This doesn't really apply to fully depreciated cars like an early NSX, but for the most part it's true.
As for what your friend can do, it all depends on credit. I'm gonna assume it sucks since he's stuck with a crappy loan in the first place. If that is the case, the best thing you can do is keep paying until it is paid off and drive it till the wheels fall off.