I'm here to embrace physics. Small Car + Big Truck = Death.
Edit: I don't understand why this is getting downvoted. Americans aren't going to give up their gas guzzler for a smaller vehicle (although I agree that they should at least not have a gas guzzler), and even if they did, not everyone would. Sure, you'll probably have points in the replies (once I get some), but I'm going off of an IIHS perspective. If a small vehicle gets into an accident (assuming it's head on/moderate/overlap) with another vehicle (as most American vehicles are either SUVs or Trucks [yes, I know an SUV is technically a truck, but that's not the point]), that person in the smaller vehicle will most likely be dead or seriously injured in that crash. It doesn't have to be particularly fast for a weight problem to show a big impact.