The effects are felt elsewhere, too. Most manufacturers aren't going to design two versions of a model for two regions, the energy efficient one, and the less energy efficient one. They'll just work to make one that fits the more stringent one. California has been one of the biggest drivers of EE nationwide because of that.

It's interesting to see it in practice too; if you move to California and bring a car, part of the registration process is to check the car and make sure it indicates it meets California requirements in design and build (not just smog testing; they do that too, but the actual registration/titling will involve them popping the hood and checking the car has the right markings). And basically every modern car does.