+1 that it was already broken.

I don't even own a rack, and I drive to ride more often than I ride from home. The only thing that has EVER happened to my bike from riding in the car, is once one of the wheel quick-releases got pulled partially open. Luckily for me the wheel didn't come off and I noticed it when the brakes started rubbing.

Lots of people show up at the club rides with their bikes in their cars ... sometimes with both wheels off and the frame stuck in the trunk. Basically the only thing on a bike that's meant to move with no more force than it takes to slide on and off carpet is the quick-releases, so as long as you check those (and as lph said, keep the drivetrain up, for the sake of your carpet as well as your bikes) you're fine.