The list is endless, as is any list of government regulations, so we don't really have the room to list out all of the regulations inhibiting rapid growth in the automotive industry. The EPA, Clean Air Act, among many state regulations simply delay the process for new innovate hybrid and electric cars to be introduced into US circulation.
Take a quick look at some of the models offered from these car companies around the world.
http://microsites.audi.com/e-tron/index.html?locale=fr_FR#/intro
http://www.bmw.com/com/en/insights/technology/efficientdynamics/phase_2/...
http://www.gassavers.org/f63/reasons-efficient-cars-arent-offered-in-the...