This is really too bad. These backover injuries are largely preventable, and the required camera and display systems are relatively inexpensive.
In fact, with the technology getting cheaper every day, we will eventually get to the point where almost all new cars will have backup cameras. But without a federal mandate, it will take much longer to get to that point, and we will have needless injury and loss of life in the meantime.
The original 2008 legislation is available here:
http://www.gpo.gov/fdsys/pkg/PLAW-110publ189/pdf/PLAW-110publ189.pdf
I would note that the law says that DOT *shall* revise FMVSS to improve rear visibility. It is not optional, and NHTSA's failure to act in a timely way is a real problem. (Contrast that with the section on power window entrapment, where the law merely says that DOT shall *consider* appropriate standards.)
The law as written also allows NHTSA quite a bit of leeway to prescribe other technologies, such as mirrors or sensors, and to make different standards for different classes of vehicles and to prioritize phase-in.
Starting the phase-in with larger SUVs and pickups would probably address some of the arguments of opponents of this rule, who feel that it's "over-reach by Big Government" (or whatever) to require this on every single vehicle down to a tiny Mini Cooper.
Safety mandates like this can also be valuable because they cut through all of the games that automakers like to play with trim levels and option packages. For example, we wanted a rear-view camera for our new Subaru Outback, and it was available, but only if we also added an automatic transmission and a moonroof package, neither of which we wanted, and which would have added thousands to the price of the car, instead of just the relatively small cost of the camera system. (There's already a display screen.) That kind of packaging might make sense for convenience and luxury features, but it doesn't make sense for safety features.