I've discussed this issue extensively on another post on this site. This will be my last post on this for a while.
At the end of the day, developers need to make money. Many are not. If your alarm bells aren't ringing yet, then let's play a game. Find me a publicly traded developer who has been doing well over the past few years. EA Games, Ubisoft, THQ, Nintendo, Sony, all have done poorly. I bet if Microsoft released separate component data on video games, they'd report doing poorly as well. The only publicly traded company that seems to be doing well is ActivisionBlizzard... and yet, Vivendi wants to sell their majority stake. Something smell fishy when a parent company wants to sell the most profitable game publisher/developer in the industry? I think so.
Now, just for fun, look at game stop's financial statements and see how well they've been doing comparatively. Yeah, bet you got a kick out of that, right?
Do I think that used games are the only reason that the video game industry is tanking as a whole? Heck no, but let's not kid ourselves into thinking they're saving it.
Also, everyone uses the car analogy as a defense for used games but it's quite possibly the worst analogy in the second hand market to use because it's completely different economically.
It differs in price and consumer group. It differs in frequency and volume of resales. It differs in the fact that condition of cars matters much more than the condition of games. It differs in life cycle and selling window. Let's also not forget the fact that you need to own a car to benefit from it, where as after you beat a game, you've pretty much already absorbed all of the utility you'll ever get out of it.
The business models between cars and games are also completely different. Car manufacturers (and by extension dealers) make money off of replacement parts, service, and car loans. They tend to make very little actual profit off the sale of a new car (except for the luxury dealers). In other words, they have a constant stream of income AFTER the sale of a car. If a person sells the car used, the next owner will typically need parts, service, and car loans as well.
On the flip side, game developers make their money through the initial sale and not through subsequent services. They've been switching to more of a service model (DLC, call of duty elite, pay-to-play, and micro transactions), but you all know how well gamers take to being nickled and dimed.